JP2010150970A - Spark ignition direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark ignition direct injection engine having excellent ignition stability and combustion stability even if ignition is performed on and after a compression top dead center, immediately raising temperature of an engine and temperature of a catalyst, and having excellent exhaust emission control performance, during the specific operation of the engine. <P>SOLUTION: This spark ignition direct injection engine 1 includes a multi-hole injector 7, an ignition plug 6, and the like. The top surface 14 of a piston 4 is formed into a pent roof shape. Control is performed such that during the specific operation of the engine 1, fuel is injected twice in a suction stroke and in the latter half of a compression stroke, and ignition is performed on and after the compression top dead center. Spray F2 of fuel injected from a second nozzle hole 28b in the latter half of the compression stroke collides with the first inclined surface (slant surface) 42 of the top surface 14, and is subsequently transferred around the electrode 6a of the ignition plug 6. A weir-shaped portion 50 is formed in a portion between two exhaust valves 20, 20 on the ceiling 13 of a combustion chamber 15 in order to stay the spray F2 around the electrode 6a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention includes a spark ignition type in which an injector disposed at a peripheral portion of a combustion chamber and a spark plug disposed substantially at the center upper portion of the combustion chamber, and fuel is injected at a timing that ends in the latter half of the compression process. It relates to a direct injection engine.

  In order to achieve good stratified combustion in the present invention, it has been studied to devise a shape of the top surface of the piston so that the injected fuel is stably supplied around the electrode.

For example, in Patent Document 1, a concave portion deeper than the bowl is formed in the range from the intake valve side to the approximate center of the piston on the top surface of the piston having a spherical bowl recessed at the center, By this recess, the fuel injected near the compression top dead center is guided to the electrode side.
JP 2000-130171 A

  By the way, in recent years, exhaust gas regulations for automobiles have become strict due to increasing interest in environmental problems, and in the development of automobiles, improvement in exhaust gas purification performance has become an important concern along with improvement in fuel consumption.

  Normally, a catalyst is disposed in the exhaust path of an automobile to purify exhaust gas, and components such as HC and CO contained in the exhaust gas are purified by the oxidation-reduction action of the catalyst. Yes.

  However, in order to activate this catalyst so that an appropriate oxidation-reduction action can be exerted, for example, a temperature of 200 ° C. or higher is necessary, so that it is immediately after the engine is cold started or when the engine is warm. However, if the temperature is low and the catalyst is not activated, such as when the deceleration fuel cut continues for a long time, how to quickly increase the temperature is an issue. It has been studied to delay the ignition timing as much as possible to discharge exhaust gas having a high amount of heat and raise the temperature of the catalyst by the heat.

  However, when the ignition timing is delayed and the mixture is ignited in the expansion stroke after the compression top dead center where the air-fuel mixture expands adiabatically, the temperature and pressure in the combustion chamber decrease as the ignition timing is delayed. Therefore, it becomes difficult to ignite, and it becomes difficult to ensure ignition stability. Furthermore, there is a problem that it is difficult to ensure combustion stability because the flame is difficult to propagate even if ignition is possible.

  Further, when the engine is cold immediately after the engine is cold, the inside of the cylinder is not warmed and the temperature is low. If the injected fuel adheres to the inner wall or the like of the cylinder, there is a risk of causing bad effects such as poor combustion or mixing into the engine oil. is there.

  In this regard, if the shape of the top surface of the piston is devised as in the above-mentioned Patent Document 1, the spray of fuel can be stably transferred around the electrode, so that the problems of ignition stability and combustion stability are to some extent. Can be solved.

  However, even if the fuel spray can be stably transferred around the electrode, it is dispersed from the electrode, and it is difficult to distribute the air-fuel mixture around the electrode.

  The present invention has been made in view of the above points, and an object of the present invention is to stably form a relatively rich air-fuel mixture mass around the electrode of the spark plug, and to achieve stable ignition and stable combustion. The object is to provide a spark-ignition direct injection engine excellent in performance. In addition, the object of the present invention is to provide excellent ignition stability and combustion stability even when ignited after compression top dead center, can quickly increase the temperature of the engine and the catalyst, and is excellent in exhaust gas purification performance. Another object is to provide a spark ignition direct injection engine.

  In order to achieve the above object, according to the present invention, a weir-like portion is formed on the ceiling of the combustion chamber so that the spray that collides with the top surface of the piston and moves around the electrode of the spark plug stays around the electrode. Provided.

  Specifically, the present invention provides two intake valves and two exhaust valves respectively disposed in parallel on the ceiling portion of a pent roof-shaped combustion chamber, and is disposed on a peripheral portion of the combustion chamber. An injector that injects fuel into the combustion chamber from between the intake valves, an ignition plug that is disposed substantially at the center upper portion of the combustion chamber and has an electrode protruding into the combustion chamber, and a piston that defines a lower portion of the combustion chamber. A spark-ignition direct injection engine, in which the fuel spray injected at the end of the second half of the compression process is directed to a substantially central portion of the combustion chamber in plan view, and the intake valve and the exhaust valve are In the front view seen from the left and right, the direction of the injection port of the injector is set so as to collide obliquely with the top surface of the piston, and the portion between the two exhaust valves in the ceiling portion of the combustion chamber Bottom orientation of electrode It is characterized in that the barrier portion is provided projecting up.

  That is, in the present invention, first, the fuel spray injected at the end of the second half of the compression process is directed to the substantially central portion of the combustion chamber in a plan view, and the intake valve and the exhaust valve are viewed to the left and right. In the front view, the direction of the injection nozzle of the injector is set so as to collide obliquely with the top surface of the piston.

  Specifically, in a combustion chamber with a relatively small volume, fuel is injected obliquely downward from the injector toward the front of the approximate center of the top surface of the piston, and the spray collides diagonally with the top surface of the piston. Then, while weakening the momentum, it flows toward the electrode side of the spark plug located substantially above the center of the combustion chamber.

  Since the tip of the electrode in the direction in which the spray flows is provided with a weir-like portion that protrudes to a position below the electrode, the flow of the spray is blocked by the weir-like portion, and the spray does not disperse around the electrode Will stay at a high probability.

  In particular, the latter half of the compression process is after a period of 3/4 of the compression process has elapsed. During specific operation of the engine, fuel is injected at this timing, and ignition is performed after the compression top dead center. It is effective to control.

  In this way, when fuel is injected at the above-mentioned timing in the latter half of the compression process and ignition is performed after the compression top dead center, that is, ignition is performed in the expansion stroke, ignition and combustion become difficult. Therefore, it is possible to stably form an air-rich mixture of air-fuel mixtures, and effectively suppress poor ignition and poor combustion. Therefore, for example, at the time of cold start of an engine in which exhaust gas purification is not successful because the temperature of the catalyst is low, the exhaust gas having a high calorific value can be discharged and the temperature of the catalyst can be quickly raised. Thus, the exhaust gas purification performance can be improved.

  Specifically, the top surface of the piston may be formed on a slope facing the injector side along the ceiling of the combustion chamber so that the spray collides with the slope.

  If it does so, the volume of a combustion chamber will become relatively small by the part which made the top surface the pent roof shape, and it can raise a compression rate. Then, by causing the injected fuel to collide with one of the slopes, the collided spray flows along the slope and is smoothly transferred around the electrode, and the mixture mass is more stably around the electrode. Can be formed.

  More specifically, at the timing when the spray reaches the periphery of the electrode, it is preferable to set so that a virtual extended surface obtained by extending the inclined surface from the upper edge thereof intersects the weir-shaped portion.

  In other words, since the top surface of the piston is raised even after the fuel is injected, the direction of flow of the spray that collides with the top surface is restricted to some extent by the top surface in the ascending process. And, at the timing when the spray reaches around the electrode, the virtual extension surface extended from the upper edge of the slope intersects the weir-like portion, that is, the lower end of the weir-like portion is located below the virtual extension surface. If so, most of the spray is blocked by the weir-like portion and stays around the electrode, so that the diffusion of the spray can be effectively suppressed.

  In particular, if the width of the end portion on the center side of the combustion chamber in the weir-like portion is formed larger than the width of the end portion on the outer peripheral side, the width of the end portion on which the spray strikes is relatively large. The spray can be effectively blocked and the width of the end of the non-sprayed end is relatively small, ensuring a relatively large space between the exhaust valves located on both sides Therefore, it is possible to effectively prevent the weir-like portion from interfering with the exhaust and causing a large exhaust resistance.

  Further, the injector is provided with a plurality of nozzle holes, and at least one of the nozzle holes is set in the above-described direction, and the intake process and the latter half of the compression process are performed during the specific operation of the engine. It is also possible to perform fuel injection in a plurality of times.

  If it does so, a fuel can be disperse | distributed and injected from a some nozzle, and vaporization atomization of a fuel can be accelerated | stimulated. For example, if the fuel is injected once in each process, the fuel injected in the intake process stays long in the combustion chamber having a relatively large volume and promotes vaporization and atomization. A relatively uniform air-fuel mixture can be formed. On the other hand, in the latter half of the compression process, the combustion chamber has a relatively small volume and the internal pressure is rising, so that the injected fuel can be easily transferred without being greatly dispersed because its penetration force is weakened, A relatively rich air-fuel mixture mass can be formed around the spark plug.

  Still further, swirl flow generating means for generating a swirl flow in the combustion chamber is provided, and the weir-like portion is formed in a range excluding the central portion and the outer peripheral portion of the combustion chamber in the radial direction of the ceiling portion. May be.

  By doing so, it is possible to generate a swirl flow in the combustion chamber including when the engine is cold started, and to promote vaporization of fuel in the combustion chamber. In particular, the swirl flow around the combustion chamber is relatively strong, but the weir-like part is formed in the range excluding the outer peripheral part, so that the weir-like part does not weaken the momentum of the swirl flow. That's it. Accordingly, since the vaporization and atomization of the fuel can be promoted in the periphery of the combustion chamber, the flame propagation becomes stable even in the expansion stroke where the combustion is unstable, and the combustion stability can be improved. It is also possible to effectively prevent fuel droplets from adhering to the cylinder inner wall.

  Note that the above specific operation time of the engine means that the ignition timing is to be set after the compression top dead center, and the catalyst is inactive even when the engine is relatively warm. It is during engine operation or when the engine is cold.

  During such engine operation, ignition stability and combustion stability are ensured even when ignition is performed after compression top dead center. Therefore, exhaust gas temperature can be quickly increased by ignition after compression top dead center. In addition, the heat receiving capacity of the combustion heat of the engine body can be increased, the combustibility and the catalyst purification performance can be improved, and the exhaust gas purification performance can be improved.

  As described above, according to the present invention, it is possible to stably form a relatively rich mixture of air-fuel mixture around the electrode, so that the ignition timing is delayed to ignite after compression top dead center. Even in this case, the ignition stability and the combustion stability are excellent, and the exhaust gas purification performance can be improved by quickly increasing the catalyst temperature and the engine temperature during specific engine operation.

  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.

(overall structure)
FIG. 1 shows an overall configuration of a spark ignition direct injection engine 1 (also simply referred to as an engine 1) in the present embodiment. The engine 1 is a multi-cylinder gasoline engine mounted on a vehicle. In addition, since the main structures of each cylinder are the same, in the same figure, it represents about one cylinder.

  The engine 1 includes a cylinder block 2, a cylinder head 3, a piston 4, a crankshaft 5, a spark plug 6, an injector 7, an intake system 8, an exhaust system 9, an engine control unit 10 (also referred to as an ECU 10), and the like. Thus, for example, the combustion is performed under a relatively high compression ratio of about 14 compression ratio. In the normal operation state, the air-fuel mixture is made uniform from the low load operation region to the high load operation region, and combustion is performed (uniform combustion). In the cold start), the air-fuel mixture is set to be weakly stratified and burned (weakly stratified combustion).

  First, the cylinder block 2 will be described. A plurality of cylinders 11, 11,... Are provided inside the cylinder block 2, and the upper part of each cylinder 11 is closed by the cylinder head 3 disposed on the upper part of the cylinder block 2. It is peeling. In each cylinder 11, as shown in detail in FIG. 2, a piston 4 is accommodated so as to reciprocate along its axis Z. Each piston 4 is connected to a crankshaft 5 via a connecting rod, and the crankshaft 5 is rotationally driven by these reciprocating motions. A crank angle sensor 12 for detecting the crank angle is disposed at one end of the crankshaft 5. And the combustion chamber 15 is formed in the upper part of each cylinder 11 by dividing up and down by the ceiling part 13 formed in the bottom face of the cylinder head 3, and the top face of each piston 4. As shown in FIG.

  The combustion chamber 15 has a pent roof shape in which the ceiling portion 13 has a triangular roof shape, and a pair of inclined surfaces of the ceiling portion 13 are an intake side where the intake system 8 is provided and an exhaust side where the exhaust system 9 is provided. It faces. The top surface 14 of the piston 4 is formed in a pent roof shape so as to correspond to (belong to) the ceiling portion 13, and a cavity 16 is formed at a substantially central portion thereof. The ceiling portion 13 of the combustion chamber 15 and the top surface 14 of the piston 4 will be described later separately.

  As shown in FIG. 3, two openings 19 a and 19 b each opened and closed by the intake valve 18 are opened in parallel on the slope on the intake side of the ceiling portion 13, and two openings 19 a and 19 b are opened in parallel. One end of each of the two intake ports 19, 19 is connected. Each intake port 19 extends obliquely upward from the combustion chamber 15 and is connected to an opening formed on one side surface of the cylinder head 3.

  On the other hand, two openings 21a and 21a that are opened and closed by the exhaust valve 20 are opened in parallel on the slope on the exhaust side of the ceiling portion 13, and two exhaust ports 21 and 21a are opened in parallel with these openings 21a and 21a. One end of each 21 is connected. The exhaust ports 21 merge together in the middle, extend substantially horizontally from the combustion chamber 15, and are connected to an opening formed on the other side surface of the cylinder head 3.

  The intake valve 18 and the exhaust valve 20 respectively open and close the openings 19a, 19b, and 21a at predetermined timings for each cylinder 11 by the intake cam shaft 22 and the exhaust cam shaft 23 that are rotationally driven by the crankshaft 5, respectively. It has become. The intake camshaft 22 is provided with a variable valve mechanism 25 capable of continuously changing the rotation phase with respect to the crankshaft 5 within a predetermined angle range. The intake valve 18 is activated by the operation of the variable valve mechanism 25. The opening and closing timing of the can be changed.

  The spark plug 6 is disposed in the cylinder head 3 so as to be positioned substantially at the center of the upper portion of the combustion chamber 15, and the electrode 6 a provided at the tip thereof is surrounded by the intake and exhaust valves 18 and 20. Projecting into the combustion chamber 15 from a substantially central portion of the portion 13. On the other hand, an ignition circuit 26 is connected to the base end portion of the spark plug 6, and electricity is supplied to the spark plug 6 at a predetermined ignition timing for each cylinder 11.

  The injector 7 is disposed in a lower portion between the two intake ports 19, 19 at the peripheral edge of the combustion chamber 15, and is provided with an injection hole 28 so that fuel can be directly injected into the combustion chamber 15. The leading end faces the combustion chamber 15 from between the two intake valves 18 and 18. The injector 7 is a multi-hole type injector 7 having a plurality of nozzle holes 28, and in this embodiment, six nozzle holes 28a, 28b, 28c,... (Also simply referred to as nozzle holes 28) are provided. The directions of the nozzle holes 28a, 28b, 28c,... Will be described later separately.

  A fuel distribution pipe 30 common to each cylinder 11 is connected to each injector 7, and fuel adjusted to a predetermined pressure is distributed and supplied from a fuel supply system 31 at a predetermined timing.

  The intake system 8 includes an intake passage 32, a surge tank 33, an air cleaner, and the like. The intake passage 32 is provided between the intake port 19 and the surge tank 33, and the air filtered by an air cleaner (not shown) passes through the surge tank 33, the intake passage 32, and the intake port 19 in this order, so that each cylinder 11 It is fed to the combustion chamber 15.

  As shown in FIG. 3, the intake passage 32 is provided with a pair of branch passages 32 a and 32 b that are bifurcated in the middle, and these branch passages 32 a and 32 b are connected to the respective intake ports 19 and 19. Yes. In one branch passage 32a, a flow rate control valve 35 for changing the flow rate of the supplied air is provided in order to form a swirl flow in the combustion chamber 15.

  The flow control valve 35 has a valve body that closes the flow path of the branch passage 32a. The valve body is supported in the branch passage 32a so as to be tiltable. When the tilt control is performed in the closing direction, the flow path is narrowed. Thus, the intake air introduced into the combustion chamber 15 from the two intake ports 19 and 19 is relatively strong and tends to be offset. Then, as shown by the arrow line in FIG. 3, a swirl flow swirling in the circumferential direction is formed in the combustion chamber 15. As in the present embodiment, when the intake air with vigor is introduced from the opening 19b located on the traveling side in the clockwise direction when the cylinder axis Z direction is viewed from above, a swirl flow swirling in the clockwise direction is formed. Will be.

  The exhaust system 9 includes an exhaust manifold 36, a catalytic converter 37, an exhaust pipe 38, a muffler, and the like. The exhaust manifold 36 is connected to the exhaust port 21 of each cylinder 11, and a catalytic converter 37, an exhaust pipe 38, and a muffler (not shown) are sequentially connected to the downstream side thereof.

  The catalytic converter 37 is provided with a catalyst for purifying components in exhaust gas such as HC and CO by oxidation-reduction action. However, since the purification function of this catalyst is not exhibited in an inactive state at a low temperature, it is necessary to activate the catalyst at a predetermined temperature of, for example, 200 ° C. or higher.

  The ECU 10 includes hardware such as a CPU, ROM, and RAM and software such as various control programs in order to control the operation of the engine 1.

  Specifically, the ECU 10 includes an ignition control unit 10 a that controls the ignition timing of the spark plug 6, a fuel injection control unit 10 b that controls the fuel injection timing of the injector 7, and an intake air flow rate that controls the amount of tilt of the flow control valve 35. A control program such as the control unit 10c is provided, and the ECU 10 determines whether the engine 10 is based on signals input from various devices such as a crank angle sensor 12, an accelerator sensor, a brake sensor, and a temperature sensor attached to various parts of the engine 1. 1 is determined, and the variable valve mechanism 25, the ignition circuit 26, the injector 7, the flow control valve 35, and the like are controlled. For example, the swirl flow in the combustion chamber 15 is generated by the flow rate control valve 35 being controlled by the intake flow rate control unit 10c (swirl flow generating means).

  Next, the control of the engine 1 performed mainly by the ECU 10 will be described.

  In the engine 1, during a normal operation in which the catalytic converter 37 in the exhaust system 9 is functioning properly, the injector 7 is operated in the intake process, particularly in the first half, regardless of the operation state, and the combustion chamber 15. The air-fuel mixture is made uniform so that the entire air-fuel ratio becomes a predetermined value, and ignition is performed in the latter half of the intake process to perform combustion. In this case, the flow rate control valve 35 of the intake port 19 is tilt-controlled according to the load state of the engine 1 so that a tumble flow or a swirl flow is formed in the combustion chamber 15. The fuel atomization is promoted by using the flow.

  On the other hand, at the time of cold start when the temperature is low and the catalyst is in an inactive state, a weakly stratified mixture is generated in the combustion chamber 15 in order to quickly activate the catalyst by increasing the amount of exhaust gas exhausted. Combustion is performed by igniting after compression top dead center (for example, −15 ° BTDC).

  That is, as shown in FIG. 4, fuel injection is performed in a plurality of times in the intake process and the latter half of the compression process. In the present embodiment, fuel injection is performed twice, and the hatched area in the figure indicates the fuel injection timing.

  In the first combustion injection (first injection), fuel is injected in the first half of the intake process in order to promote vaporization and atomization of the fuel, thereby forming a relatively uniform air-fuel mixture. In the second fuel injection (second injection), in order to transfer the injected fuel as much as possible around the electrode 6a of the spark plug 6 (also simply referred to as around the electrode 6a), 3/4 of the compression process. The fuel is injected at a timing (for example, 35 ° BTDC) at which the injection ends after the period has elapsed, and a relatively rich air-fuel mixture lump is formed around the electrode 6a.

  In this case, the flow rate control valve 35 of the intake port 19 is largely tilt-controlled in the closing direction such as completely closing the flow path by the intake flow rate control unit 10 c of the ECU 10, and a swirl flow with a relatively strong momentum is generated in the combustion chamber 15. As the swirl flow is strengthened, vaporization and atomization of the fuel of the first injection is promoted, and the adhesion of the fuel of the second injection to the cylinder inner wall is effectively prevented. It can be done.

  When ignition is performed in the expansion stroke after the compression top dead center in this way, the volume of the combustion chamber 15 increases and the temperature and pressure of the air-fuel mixture decrease, so that ignition and combustion become unstable, but the electrode 6a By forming a relatively rich mixture of air-fuel mixture around it, it has excellent ignition stability, and by forming a relatively uniform air-fuel mixture around it, it is easy to propagate the flame and also improves combustion stability. It will be excellent.

  Then, when a predetermined condition is satisfied, for example, when a predetermined time elapses or the temperature of the catalyst measured by the temperature sensor reaches a predetermined temperature, the setting is switched to the previous normal operation setting by the control of the ECU 10. It is configured.

  By the way, the direction of the nozzle hole 28 of the injector 7 is as described above. In the engine 1, uniform combustion is performed during normal operation, and weak stratified combustion is performed during cold start. It is set to respond well.

  For example, FIG. 5 schematically shows a view of the front end portion of the injector 7 that is injecting fuel as seen from the front. As shown in FIG. 5, each injection hole 28 has a front end portion of the injector 7. Are formed symmetrically with respect to the vertical reference line H extending in the vertical direction through the approximate center in the left-right direction, and a first nozzle hole 28a located on the vertical reference line H is provided on the uppermost side. Two second nozzle holes 28b and 28b are provided directly below the first nozzle hole 28a so as to be separated from the vertical reference line H on both the left and right sides. On the lower side, two third nozzle holes 28c and 28c are provided on both sides from the vertical reference line H, and are positioned in line symmetry with a distance larger than the second nozzle hole 28b and away from both sides of the vertical reference line H. 28c, located just below the vertical reference line H just below 28c One fourth injection port 28d is provided for. In addition, the arrow line in a figure represents directions, such as up and down.

  A conical spray having a spread of about 10 ° to 20 ° is formed from each nozzle 28, and the piston 4 is lowered during the normal operation or the first injection at the cold start. Since the fuel is injected into the combustion chamber 15 having a relatively large volume, each spray is spread radially without overlapping each other so that the injected fuel is widely dispersed throughout the cylinder 11. The direction of the nozzle 28 is set.

  At the time of the second injection at the cold start, as shown in FIG. 2, the fuel is injected into the combustion chamber 15 in which the piston 4 is lifted and has a relatively small volume. By making good use of the fuel, the fuel is transferred around the electrode 6a.

  Specifically, as shown in FIG. 6, the first nozzle hole 28 a is directed toward the substantially central portion of the combustion chamber 15 in a plan view, and as shown in FIG. 2, the front face when the intake valve 18 and the exhaust valve 20 are viewed from side to side. In view, the direction of the fuel F <b> 1 injected therefrom collides with the inner wall surface of the cavity 16. Similarly, the second injection holes 28b, 28b are directed to the substantially central portion of the combustion chamber 15 while being slightly shifted left and right in the plan view, and the fuel F2 injected therefrom is the intake side of the piston 4 in the front view. The direction is set so as to obliquely collide with a slope (first slope 42 described later) facing the (injector 7 side). The third nozzle holes 28c, 28c are oriented such that the fuel F3 injected therefrom is shifted further left and right than the second nozzle holes 28b and obliquely collides with the top surface 14 including the first inclined surface 42. The nozzle hole 28d is set to face the lower side than these nozzle holes 28a, 28b,.

  For example, FIGS. 7A to 7D show the displacement of the fuel droplets injected from the second injection port 28b, but are compressed during the second injection and the internal pressure of the combustion chamber 15 increases. Therefore, the penetration force of the spray is relatively weak, and when the fuel injected as shown in (a) collides with the first slope 42 as shown in (b), the momentum during injection decreases. As shown in (c) and (d), it flows along the vicinity of the surface thereof, and is transferred around the center of the top surface 14 of the piston 4, that is, around the electrode 6a. Become.

  As a result, a relatively rich air-fuel mixture is formed around the electrode 6a, but after reaching around the electrode 6a, a part further flows or diffuses further to the electrode 6a. There was a limit to improve ignition stability by distributing high-concentration air-fuel mixture.

  Therefore, a dam-like portion 50 is provided on the ceiling portion 13 of the combustion chamber 15 so that the fuel spray can be stably kept around the electrode 6a.

(Main part configuration)
Next, the features of the present invention will be described in detail.

  FIG. 8 shows the piston 4. The top surface 14 of the cylindrical piston 4 is formed in a pent roof shape so as to correspond to the ceiling portion 13 of the combustion chamber 15, and has a cylindrical axis (cylinder axis Z ), A flat base surface 41 orthogonal to the first surface 42, a first slope 42 and a second slope 43 extending obliquely upward from the base surface 41, and a ridge surface 44 connected to the upper edge of the first slope 42 and the second slope 43, respectively. And.

  On the outer peripheral portion of the top surface 14 of the piston 4, a base surface 41 extends in an annular shape (also referred to as a flange portion 41b) so that a swirl flow can smoothly flow. Since the swirl flow formed along the cylinder inner wall is held without significant attenuation by the flange portion 41b, the fuel injected at the time of the first injection during normal operation or cold start is vaporized and atomized. It is promoted and a more uniform air-fuel mixture can be formed, and the adhesion of fuel to the cylinder inner wall can be reduced.

  In particular, in the case of the fuel injected at the time of the second injection, the temperature of the inner wall of the cylinder is not increased, and if the fuel adheres, there is a strong risk of causing a combustion failure or mixing into the engine oil. It is possible to effectively reduce the adhesion of fuel to the inner wall.

  A cavity 16 having a substantially elliptical opening edge is formed in a concave portion at a substantially central portion of the top surface 14. The inner wall surface of the cavity 16 is flush with the base surface 41 and has a substantially disk-shaped bottom surface 16a having a smaller diameter than the opening edge, and the outer edge of the bottom surface 16a is connected to the periphery and the opening edge. And a curved side surface 16b that is smoothly curved.

  In the engine 1, combustion is performed under a relatively high compression ratio of about 14 compression ratio, so that the space between the ceiling portion 13 and the top surface 14 of the piston 4 is near the top dead center where ignition is performed. Although considerably smaller than the conventional one, the ignition stability and the combustion stability are improved by positioning the cavity 16 below the spark plug 6 and securing a space around the electrode 6a.

  The piston 4 is disposed in the cylinder 11 so that the first inclined surface 42 faces the intake side where the injector 7 is provided and the second inclined surface 43 faces the exhaust side.

  On the other hand, FIG. 9 shows the ceiling portion 13 of the combustion chamber 15, and specifically, two exhaust ports 21, 21 of the ceiling portion 13 are connected between the two exhaust valves 20, 20. A dam-like portion 50 is formed so as to protrude downward from a portion between the openings 21a and 21a.

  The weir-like portion 50 is formed in a range excluding the central portion and the outer peripheral portion of the combustion chamber 15 in the radial direction of the ceiling portion 13, in other words, at a portion near the spark plug 6 between the two openings 21a and 21a. Has been. Since it is formed in a range excluding the outer peripheral portion, it is not necessary to weaken the force of the swirl flow at the weir-like portion 50.

  And the dam-like part 50 continues to both opening parts 21a and 21a, and is connected to the vertical wall surface 50a which faces the spark plug 6 side so that it may spread along the cylinder axis Z from the ceiling part 13, and the lower end edge of this vertical wall surface 50a. And the end of the combustion chamber 15 on the center side, that is, the width of the vertical wall surface 50a is the end of the combustion chamber on the outer peripheral side, that is, the tapered surface. 50b is larger than the width of the part connected to the ceiling portion 13. Moreover, the lower end of the vertical wall surface 50a protrudes below the lower end of the electrode 6a.

  The reason why the tapered surface 50b having a large inclination is formed and the width of the end portion on which the spray does not hit is relatively small is that the exhaust valves 20 and 20 and the openings 21a and 21a disposed on both sides thereof. This is because a relatively large space is ensured between them to prevent a large exhaust resistance from being generated by the dam-like portion 50 during exhaust.

  This dam-like portion 50 functions in particular to keep the fuel spray injected from the second injection port 28b around the electrode 6a.

  That is, FIG. 10 shows changes in the spray from the second nozzle holes 28b and 28b during the second injection, and FIG. 10A shows the timing at which the fuel injection from the second nozzle 28b ends (for example, (35 ° BTDC), (b) shows the timing (for example, 15 ° BTDC) when the spray reaches around the electrode 6a. The timing at which the spray reaches the periphery of the electrode 6a depends on the state of the engine 1, but can be, for example, a timing at which the crank angle has advanced by 15 ° or more from the timing at which fuel injection is completed.

  As shown in (a), at the timing when the fuel injection is completed, the piston 4 is still positioned relatively below, and the spray of injected fuel collides with the first slope 42 in the upward process. Then, the momentum of the injection is weakened, and the fuel spray is transferred to the electrode 6a side along the rising first slope 42.

  Then, as shown in (b), at the timing when the spray reaches around the electrode 6a, a virtual extension surface M (virtual extension surface M) in which the first slope 42 is extended from the upper end edge toward the ceiling portion 13 side. ) Is set so as to intersect with the weir-like portion 50, so that the spray is regulated by the first inclined surface 42 or the cavity 16 in the lower part, and the front in the traveling direction is on the vertical wall surface 50 a of the weir-like portion 50. Since it is blocked, most of the spray stays there and a relatively rich air-fuel mixture is distributed around the electrode 6a in a lump. At this time, since the width of the vertical wall surface 50a of the weir-like portion 50 is formed to be relatively large, spraying can be effectively blocked.

  At this time, as shown in FIG. 11, the spray of fuel injected from the first nozzle hole 28a (indicated by the arrow line F1 in the figure) is sprayed from the second nozzle holes 28b and 28b (in the figure, indicated by the arrow line F2). The latter spray is pulled by the former spray, and the spray from the second nozzle hole 28b is easily transferred around the electrode 6a.

  As described above, according to the present invention, since the fuel spray is received by the weir-like portion 50, a relatively rich mixture mass can be stably formed around the electrode 6a. Even when the timing is delayed and ignition occurs after compression top dead center, it has excellent ignition stability and combustion stability. During specific operation of the engine, the temperature of the catalyst and the temperature of the engine 1 are quickly increased to exhaust gas. It becomes possible to improve the purification performance.

  The spark ignition direct injection engine 1 according to the present invention is not limited to the above-described embodiment, and includes various other configurations.

  For example, although the case where the cavity 16 is formed in the top surface 14 of the piston 4 is illustrated in the above embodiment, the cavity 16 may be omitted.

  Further, the number and arrangement of the injection holes of the injector 7 are not limited to the above embodiment. For example, as shown in FIG. 12, five nozzle holes may be formed, and one second nozzle hole 28 b may be formed on the vertical reference line H.

  The number of sprays may be at least once. In the above embodiment, the flow rate control valve 35 is exemplified as the swirl flow generating means. However, the present invention is not limited to this.

It is a schematic diagram showing the whole composition of the engine in an embodiment. It is a schematic sectional drawing which shows the principal part of the engine in embodiment. It is a schematic perspective view which shows the principal part of the engine in embodiment. It is a figure for demonstrating the injection timing of a fuel. It is a schematic perspective view for demonstrating the direction of the nozzle hole of an injector. It is a top view for demonstrating the direction of the nozzle hole of an injector. It is the figure which calculated | required the time-dependent state change of the droplet of the injected fuel by CFD. (A) represents the end of injection, and (b) to (d) represent the subsequent state. (A) is a plan view of the piston, (b) is a front view of the piston, and (c) is a side view of the piston. (A) is the figure which looked at the ceiling part of the combustion chamber from the combustion chamber side, (b) is XX sectional drawing of (a). It is a figure for demonstrating the flow of the spray from a 2nd nozzle at the time of 2nd injection. (A) represents the end of injection, and (b) represents the timing at which the spray reaches the periphery of the electrode. It is a schematic plan view for demonstrating the flow of the spray at the time of 2nd injection. It is a top view which shows another Example of the nozzle hole of an injector.

Explanation of symbols

1 Engine 4 Piston 6 Spark plug 6a Electrode 7 Injector 8 Intake system 9 Exhaust system 10 ECU
DESCRIPTION OF SYMBOLS 10a Ignition control part 10b Fuel injection control part 10c Intake flow volume control part 11 Cylinder 13 Ceiling part 14 Top surface 15 Combustion chamber 16 Cavity 18 Intake valve 19 Intake port 20 Exhaust valve 21 Exhaust port 28 Inlet 32 Intake passage 32a, 32b Branch passage 35 Flow control valve 37 Catalytic converter 41 Base surface 42 First slope (slope)
43 Second slope 44 Ridge surface 45 Intake valve recess 50 Weir-shaped portion H Vertical reference line M Virtual extension surface Z Cylinder axis

Claims (9)

Two intake valves and two exhaust valves respectively disposed in parallel on the ceiling of the pent roof-shaped combustion chamber, and disposed at the peripheral portion of the combustion chamber, and fuel is introduced into the combustion chamber from between the two intake valves. A spark ignition type direct injection engine comprising: an injector for injecting fuel; an ignition plug disposed substantially at the center of the combustion chamber; and an electrode having an electrode protruding into the combustion chamber; and a piston defining a lower portion of the combustion chamber. ,
The spray of fuel injected at the end of the latter half of the compression process is directed toward the substantially central portion of the combustion chamber in a plan view, and in the front view when the intake valve and the exhaust valve are viewed from side to side, The direction of the injector nozzle is set to collide diagonally with the top surface,
A spark ignition direct injection engine characterized in that a weir-like portion protruding to a position below the electrode is provided in a portion between the two exhaust valves in a ceiling portion of the combustion chamber. The spark ignition direct injection engine according to claim 1,
The latter half of the compression process is after a period of 3/4 of the compression process has elapsed,
A spark-ignition direct injection engine characterized in that fuel is injected at this timing during specific operation of the engine and ignition is performed after compression top dead center. The spark ignition direct injection engine according to claim 2,
A spark ignition type characterized in that the top surface of the piston is formed with an inclined surface facing the injector side along the ceiling portion of the combustion chamber, and the spray collides with the inclined surface. Direct injection engine. The spark ignition direct injection engine according to claim 3,
A spark ignition direct injection engine characterized in that, at the timing when the spray reaches the periphery of the electrode, a virtual extended surface obtained by extending the slope from its upper edge is set to intersect the weir-like portion. The spark ignition direct injection engine according to any one of claims 1 to 4,
The spark ignition type direct injection engine, wherein a width of an end portion on the center side of the combustion chamber in the dam-like portion is formed larger than a width of an end portion on the outer peripheral side. The spark ignition direct injection engine according to any one of claims 2 to 5,
The injector is provided with a plurality of nozzle holes, and at least one of the nozzle holes is set in the direction,
A spark-ignition direct injection engine characterized in that fuel injection is performed in a plurality of times in an intake process and a latter half of a compression process during specific operation of the engine. The spark ignition direct injection engine according to any one of claims 1 to 5,
Furthermore, a swirl flow generating means for generating a swirl flow in the combustion chamber is provided,
The spark ignited direct injection engine, wherein the weir-like portion is formed in a range excluding a central portion and an outer peripheral portion of the combustion chamber in a radial direction of the ceiling portion. The spark ignition direct injection engine according to any one of claims 1 to 7,
The spark-operated direct injection engine characterized in that the specific operation time is an operation time when a catalyst provided in an exhaust path of the engine is in an inactive state. The spark ignition direct injection engine according to any one of claims 1 to 7,
The spark-operated direct injection engine characterized in that the specific operation time is a cold operation time immediately after the engine is started.

Images