JP4609227B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine that performs ignition by discharging a fuel ignition source such as a jet flame to fuel directly injected into a combustion chamber.

  Conventionally, as disclosed in Patent Document 1, in a sub-chamber internal combustion engine, a fuel injection valve that directly injects fuel into a main combustion chamber and a fuel ignition source such as a jet flame are discharged into the main combustion chamber. An ignition device (including a sub chamber and a spark plug) for igniting the fuel injected from the fuel injection valve, and a substantially columnar shape formed in the main combustion chamber from the communication passage of the sub chamber by combustion in the sub chamber It is known that the air-fuel mixture in the main combustion chamber is torch-combusted by this jet flame. As a result, the main combustion period is significantly shortened with respect to the spark ignition type internal combustion engine, a leaner air-fuel mixture can be burned, and a highly efficient combustion that leads to an improvement in fuel consumption can be realized.

Further, as disclosed in Patent Document 2, in the combustion chamber structure of an internal combustion engine, a small-volume peripheral chamber that is communicated with the combustion chamber through a plurality of injection holes is formed at the outer peripheral edge of the combustion chamber. It is known that a flame from the peripheral chamber is ejected in the circumferential direction of the combustion chamber. In this case, the opening area of the nozzle hole on the intake port side where the rich portion of the air-fuel mixture tends to be unevenly distributed in the peripheral chamber is made smaller than the exhaust port side, or the peripheral chamber is arranged offset to the exhaust port side. Thus, rapid combustion in the rich region on the intake port side is suppressed.
JP-A-60-45716 JP 7-26961 A

  However, in the sub-chamber internal combustion engine described in Patent Document 1, as the engine load increases, abnormal rapid combustion generated due to torch combustion into a relatively rich mixture in the main combustion chamber, and abnormal rapid Due to the rise in combustion temperature accompanying combustion, there is a concern that early ignition (pre-ignition) of the main combustion chamber mixture on the heated sub chamber wall surface may occur, generating large vibrations and noise.

  Further, in the combustion chamber structure of the internal combustion engine described in Patent Document 2, the uneven distribution of the rich mixture on the intake port side is not intended, but the rich mixture is unevenly distributed on the intake port side due to a difference in operating conditions or the like. If not, combustion on the intake port side may become too slow, or on the contrary, combustion on the exhaust port side may become too fast, resulting in unstable combustion. Further, since the rich air-fuel mixture is also unevenly distributed in the vicinity of the wall surface, it is assumed that the wall flow increases and the discharge of unburned HC is relatively large.

  The present invention has been made in view of the above problems, and suppresses the occurrence of pre-ignition and stabilizes torch combustion by a fuel ignition source even in an operating condition where the fuel injection amount is large (for example, a high load operating region). The purpose is to do.

Therefore, in the present invention, a cavity provided on the piston crown surface, a fuel injection valve that is disposed substantially at the center of the combustion chamber, and directly injects fuel into the combustion chamber, is disposed in the vicinity of the fuel injection valve, and passes through the communication passage. A sub-chamber ignition device that emits a flame as a fuel ignition source into the combustion chamber and ignites an air-fuel mixture in the combustion chamber, and controls the injection timing of the fuel injection valve and the ignition timing of the ignition device An internal combustion engine comprising: a control unit; in the middle and high load ranges of the engine, the fuel injection valve performs split injection of early injection and late injection, and the early injection in the cavity and above or in the entire combustion chamber A lean air-fuel mixture is formed, and the latter injection that is injected toward the cavity stands in a cylindrical shape upward along the side wall of the cavity. And a local portion formed by the latter-stage injection, wherein the communication path of the ignition device is arranged on the inner peripheral side of the cavity in a plan view. It is characterized in that ignition by the ignition device is performed before the rich air-fuel mixture reaches the communication path of the ignition device .

According to the present invention, since a lean stratified mixture is formed in the vicinity of the communication path of the ignition device, the occurrence of abnormal rapid combustion and pre-ignition can be suppressed, and the rich formed at a position away from the vicinity of the communication path. Since the stratified mixture is ignited by the flame emitted from the ignition device, there is an effect that a stable operation can be performed even under an operation condition with a large amount of fuel injection.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of an internal combustion engine (hereinafter referred to as “engine”) 1 according to a first embodiment of the present invention. FIG. 2 shows a substantially columnar jet flame (fuel ignition source) in the main combustion chamber 4 by injecting fuel directly from the fuel injection valve 6 into the main combustion chamber 4 and then igniting the gas in the sub chamber 8. It is the figure which showed the state which formed.

The engine 1 introduces fresh air into the main combustion chamber 4 when the intake valve 3 is opened via the intake port 2. The main combustion chamber 4 includes a piston 5, an intake valve 3, an exhaust valve 10, a cylinder head inner wall, and a cylinder block inner wall.
A piston 5 that reciprocates in the cylinder is provided below the main combustion chamber 4. In FIG. 1, a circular cavity 5 a that receives the fuel injected from the fuel injection valve 6 is formed on the crown surface of the piston 5. The cavity 5a is formed with a substantially circular bottom 5b and a side wall 5c at the peripheral edge of the bottom 5b.

On the other hand, a fuel injection valve 6 for injecting fuel toward the cavity 5 a of the piston 5 is provided in the approximate center of the upper part of the main combustion chamber 4. An ignition plug 7 is disposed in the vicinity of the fuel injection valve 6. A sub chamber 8 is provided. In FIG. 1, the ignition device is configured to include the sub chamber 8 and the spark plug 7.
The fuel injection valve 6 can change the fuel injection timing and the fuel injection amount according to the operating condition (load), and can inject a part of the total fuel injection amount first and then the remaining fuel. It can be done. The fuel injection valve 6 injects a part of the total fuel injection amount first, so that a lean air-fuel mixture is formed in the entire main combustion chamber 4 as shown in FIG. 2, and then the remaining fuel is injected. Thus, a rich air-fuel mixture is formed in the cavity 5a of the piston 5 and on the upper side of the side wall 5c.

The sub chamber 8 has a smaller volume than the main combustion chamber 4 and communicates with the main combustion chamber 4 via the communication passage 9. In FIG. 1, the distal end portion of the sub chamber 8 is formed in a substantially semispherical shape, and a plurality of communication passages 9 are formed at predetermined intervals in the circumferential direction.
For this reason, a part of the fuel injected from the fuel injection valve 6 flows into the sub chamber 8 due to the compression of the piston 4 while being mixed with the air in the main combustion chamber 4. As a result, an air-fuel mixture (gas) suitable for combustion is supplied from the main combustion chamber 4 into the sub chamber 8.

Further, in the main combustion chamber 4, the fuel injected from the fuel injection valve 6 is mixed with the air in the main combustion chamber 4, thereby forming a stratified mixture having rich and lean air-fuel ratio distribution.
In FIG. 2 (A), the fuel injected from the fuel injection valve 6 into the main combustion chamber 4 forms a rich stratified mixture in the cavity 5a of the piston 5 and above the cavity side wall 5c. Is shown.

  In this case, the fuel injected from the fuel injection valve 6 mainly collides with the bottom 5b of the cavity 5a of the piston 5 and rises from the side wall 5c to the upper side in the cylinder axial direction in a substantially hollow cylindrical shape. Although not shown, the sub chamber 8 is provided at a position inside the side wall 5c of the cavity 5a of the piston 5 when viewed in plan. For this reason, a lean stratified mixture is formed in the vicinity of the fuel ignition source discharge portion (communication passage 9 of the sub chamber 8) of the ignition device, while the rich stratified mixture is formed in the communication passage 9 of the sub chamber 8. It is formed in the position away from. Note that the air-fuel ratio of the lean stratified mixture is such that no pre-ignition occurs.

In addition, when the gas in the sub chamber 8 is ignited by the spark plug 7, the air-fuel mixture in the sub chamber 8 explodes so that the fuel ignition source released into the main combustion chamber 4 has a substantially columnar shape. A torch (blown flame) is formed, and this torch enables ignition and combustion of a rich stratified mixture.
Note Fig. 2 (B) shows a reference example of the fuel injection valves 6 and the subchamber 8 was set on the side surface (side) side of the intake valve 3 near the main combustion chamber 4.

Referring again to FIG. 1, the exhaust after completion of combustion is discharged into the exhaust passage 11 by opening the exhaust valve 10. An exhaust air / fuel ratio sensor 12 is provided in the exhaust passage 11, and an exhaust purification catalyst 13 is provided downstream thereof. Further, the exhaust purification catalyst 13 is provided with a temperature sensor 14.
The intake valve 3 and the exhaust valve 10 are driven by an intake cam 15 and an exhaust cam 16, respectively. A fuel pump 17 is interposed at the intake camshaft end, and the pressurized fuel is guided to the fuel injection valve 6 through the high-pressure fuel pipe 18. The high-pressure fuel pipe 15 is provided with a fuel pressure sensor 19 that detects the fuel pressure and sends a signal to an engine control unit (ECU) 20.

The engine 1 is controlled by the ECU 20 in an integrated manner. Therefore, signals such as an air flow meter signal for detecting the intake air amount, an accelerator opening signal, a crank angle sensor signal, and a coolant temperature sensor signal are input to the ECU 20, and the fuel injection valve 6, based on these signals, Control the spark plug 7 and the like.
In FIG. 1, the fuel is not directly introduced into the sub-chamber 8 in addition to the air-fuel mixture introduced from the main combustion chamber 4, but the momentum of the torch ignition is increased and the combustion speed in the main combustion chamber 4 is further increased. In order to promote this, of course, a configuration in which reformed fuel such as gasoline or hydrogen, reformed gas, or the like is directly introduced into the sub chamber 8 may be used.

Further, although the description has been given of using the spark plug 7 provided in the sub chamber 8 as means for forming the substantially columnar fuel ignition source in the main combustion chamber 8, the invention is not limited to this. For example, the ignition device may be any device that can form a heat source capable of volume ignition in a rich stratified mixture using an apparatus that generates plasma, microwaves, or the like.
Further, in FIG. 1, it has been described that the fuel injected from the fuel injection valve 6 forms a stratified mixture with rich and lean air-fuel ratio distribution by the cavity 5 a of the piston 5, but is not limited thereto. It is not something. For example, if the fuel injection valve 6 can form a stratified mixture with rich and lean air-fuel ratio distribution in the main combustion chamber 4, the cavity 5a of the piston 5 need not be formed.

Next, with reference to FIG. 3, the distribution of the air-fuel mixture with respect to the engine load in the engine of the present invention and the conventional engine (the simplified configuration of the engine disclosed in Patent Document 1) will be described.
3A shows the distribution of the air-fuel mixture in Patent Document 1, and FIG. 3B shows the distribution of the air-fuel mixture in the present invention. These show the formation of the air-fuel mixture when the piston 5 is near the compression top dead center. The load is obtained based on, for example, the accelerator opening and the fuel injection amount from the fuel injection valve 6.

  In the engine of Patent Document 1, as shown in FIG. 3A, the crown surface of the piston is formed flat, and fuel is injected from the fuel injection valve attached to the intake manifold into the main combustion chamber during the intake stroke. By doing so, a substantially uniform mixture is formed in the entire combustion chamber. Then, a substantially columnar fuel ignition source is formed from the tip of the ignition device (subchamber with a built-in ignition plug) to ignite the air-fuel mixture.

  In this case, as the engine load increases, the fuel injection amount injected from the fuel injection valve increases, so that the air-fuel mixture concentration in the entire main combustion chamber becomes relatively rich as compared to when the load is low. Since the air-fuel mixture in the main combustion chamber is almost uniform, the air-fuel mixture concentration in the vicinity of the substantially columnar fuel ignition source has also become relatively rich, and reaches a relatively rich air-fuel mixture concentration. In some cases, abnormal rapid combustion and accompanying preignition occur.

As the engine load is reduced, the air-fuel mixture concentration in the entire combustion chamber becomes relatively lean, but there is a lean limit equivalent ratio (= 14.7 / air-fuel ratio) due to a substantially columnar jet flame. Since leaning is impossible from this equivalent ratio, the throttle is throttled to generate negative work (pump loss) at a lower load, thereby adjusting the load.
In the engine 1 of the present invention, as shown in FIGS. 3B (I) to (IV), an optimal air-fuel mixture is formed under each operating condition from low load to high load.

When the operating condition is a low load, as shown in FIGS. 3B and 3I, a substantially uniform air-fuel mixture is formed in the cavity 5a of the piston 5 and above it.
When the operating condition is in the vicinity of a medium load, a substantially uniform lean mixture is formed in the entire main combustion chamber 4 as shown in FIGS.
When the operation condition is from medium load to high load, a lean stratified mixture is formed in the vicinity of the fuel ignition source discharge portion of the ignition device as shown in FIGS. A rich stratified mixture is formed at a position away from the fuel ignition source discharge part, that is, at a position inside the cavity 5a of the piston 5 and above the cavity side wall part 5c. Under this operating condition, the fuel injection valve 6 performs early injection for injecting a part of the total fuel injection amount from the latter half of the intake stroke to the middle of the compression stroke (or the first half of the compression stroke), and the subsequent compression stroke. Late injection is performed in which the remaining fuel is injected from the middle to the latter half of the compression stroke.

The cavity 5a of the piston 5 is formed with a bottom 5b and a side wall 5c formed on the cylinder axis direction upper side from the bottom 5b, so that the fuel injected from the fuel injection valve 6 is the bottom 5b of the cavity 5a. To form an approximately cylindrical rich stratified mixture on the upper side from the side wall 5c. Further, the air-fuel ratio is lean outside the rich stratified mixture.
Further, the front end portion (communication passage 9) of the sub chamber 8 has a structure arranged in the side wall portion 5c of the cavity 5a of the piston 5 when viewed in plan, so that it is inside the rich stratified mixture having a substantially cylindrical shape. The air-fuel ratio is disposed where a stratified mixture is formed. Thereby, even when the front end portion of the sub chamber 8 becomes a high temperature state due to combustion in the main combustion chamber 4, it is possible to prevent the fuel from spontaneously igniting until ignition is performed by the spark plug 7 in the sub chamber 8. However, the ignition timing of the spark plug 7 in the sub chamber 8 is appropriate so that the rich stratified mixture can be discharged from the sub chamber 8 into the rich stratified mixture before reaching the communication passage 9 of the sub chamber 8. Set to.

  Further, a plurality of communication passages 9 formed at the tip of the sub chamber 8 are formed at predetermined intervals in the circumferential direction, and fuel ignition is performed from the communication passage 9 of the sub chamber 8 by the spark plug 7 in the sub chamber 8. The rich stratified mixture formed on the upper side from the side wall 5c of the piston 5 is ignited and burned by the substantially columnar jet flame as the source. As a result, in the vicinity of the tip of the sub chamber 8 where a lean stratified mixture is formed, abnormal rapid combustion and pre-ignition can be prevented, fuel injection amount is large, and abnormal rapid combustion and pre-ignition are likely to occur. Stable operation is possible even under conditions (above medium load).

Further, when the load is medium to high, a rich air-fuel mixture is formed in the cavity 5a of the piston 5 and on the cylinder axial direction upper side of the cavity side wall portion 5c, so that negative work due to pump loss is reduced compared to non-stratification. Therefore, the fuel consumption is good and the cylinder wall flow is reduced, so that the emission of unburned HC can be reduced.
When the operating condition is a high load, a lean stratified mixture is formed near the fuel ignition source discharge portion of the ignition device, as shown in FIGS. A rich stratified mixture is formed at a position away from the fire source discharge portion, that is, at a position inside the cavity 5a of the piston 5 and above the cavity side wall portion 5c.

The stratified mixture as shown in FIGS. 3 (B) and 3 (IV) performs early fuel injection during the intake stroke to form a lean stratified mixture over the entire main combustion chamber 4, and the fuel during the subsequent compression stroke. It is formed by performing the latter stage injection.
3 (B) and (III), the cavity 5a of the piston 5 is formed with a bottom portion 5b and a side wall portion 5c formed on the upper side in the cylinder axial direction from the bottom portion 5b. The fuel injected from the valve 6 collides with the cavity 5a, and forms a substantially cylindrical rich stratified mixture on the upper side from the side wall 5c.

  However, in FIGS. 3 (B) and (IV), the amount of fuel injected from the fuel injection valve 6 is larger than that in FIGS. 3 (B) and (III), so the inside of the cavity 5a of the piston 5 and the cavity side wall 5c. The stratified mixture formed on the upper side in the cylinder axial direction becomes richer. At this time, the air-fuel ratio is lean outside the rich stratified mixture formed on the upper side in the cylinder axial direction of the cavity side wall 5c, but it becomes rich compared to FIGS. 3 (B) and (III). Yes. Further, a stratified mixture leaner than the stoichiometric air-fuel ratio (14.7) is formed in the entire main combustion chamber 4 except at a position where a rich stratified mixture is formed.

  Next, the equivalent ratio of the air-fuel mixture to the engine load in the present invention will be described with reference to FIG. In FIG. 4, the equivalence ratio of the air-fuel mixture in the entire main combustion chamber 4 is indicated by a solid line α, and the equivalence ratio of the rich stratified air-fuel mixture formed in the cavity 5 and on the upper side in the cylinder axial direction of the cavity side wall 5c (FIG. 4B). Equivalent ratio at the position indicated by a broken line in FIG. 4) is equivalent to the broken line β and the equivalent ratio in the vicinity of the tip portion (communication path 9) of the sub chamber 8 (equivalent at the position indicated by the one-dot chain line in FIG. 4B) Ratio) is indicated by a one-dot chain line γ. Note that the equivalent ratio of the limit at which lean combustion by the jet flame from the sub chamber 8 can be performed is denoted by φL, and the equivalent ratio of the limit at which pre-ignition by abnormal rapid combustion is represented by φH.

  When the operating condition is in a relatively low load region, the air-fuel mixture is stratified above the cavity 5a as shown in FIGS. As shown in the load region of FIGS. 4A and 4I, when the load is relatively high in the low load region, the equivalence ratio of the air-fuel mixture over the cavity 5a is set to be leaner than φH in the vicinity of φH. Is done. At an extremely low load, the equivalent ratio of the air-fuel mixture above the cavity center position is set to a richer side than φL in the vicinity of φL.

  When the operation condition is in a relatively medium load region, as shown in FIGS. 3 (B) and (II), a substantially uniform mixture is formed in the entire main combustion chamber 4, but the equivalence ratio range of the mixture 4A and 4B, the lower limit value is set to a richer side than φL in the vicinity of φL, and the upper limit value is set to a leaner side than φH in the vicinity of φH. In this region, the equivalent ratio becomes rich when the load increases.

  When the operating condition is in the middle to high load region, the stratified mixture is given a concentration distribution as shown in FIGS. In this case, as shown in the load region of FIGS. 4 (A) and (III), the equivalent ratio of the main combustion chamber 4 as a whole increases relatively as the load increases. Is set to be substantially constant on the lean side from φH in the vicinity of φH, while the equivalent ratio in the cavity 5a and above the side wall portion 5c becomes relatively rich as the load increases.

  When the operating condition is in the high load region, as shown in FIGS. 3B and 4IV, the equivalence ratio of the main combustion chamber 4 as a whole increases as the load increases, as in the middle to high load regions. As shown in the load region of FIGS. 4 (A) and 4 (IV), the equivalent ratio in the sky above the center position of the cavity is set to be substantially constant on the lean side from φH in the vicinity of φH. The equivalent ratio in the sky above the portion 5c becomes relatively rich as the load increases.

Next, the behavior of the air-fuel mixture when the operating condition is equal to or higher than the medium load will be described.
FIG. 5 is a diagram showing the mixture behavior when a rich mixture is formed in the cavity 5a and on the upper side of the side wall portion 5c from the middle load to the high load region as shown in FIGS. is there.
First, the fuel injection valve 6 performs early injection in which a part of the total fuel injection amount is injected into the cavity 5a from the latter half of the intake stroke to the middle of the compression stroke (or the first half of the compression stroke) (FIG. 5 (I )). The injection timing of the early injection advances as the engine load increases in order to improve the uniformity of the lean air-fuel mixture in the vicinity of the communication passage 9 in the sub chamber 8 and realize combustion with less NOx.

  The injected fuel collides with the cavity bottom 5b, and is then guided from the cavity side wall 5c upward in the cylinder axial direction by entraining ambient air by the momentum of the spray (FIG. 5 (II)). Then, a substantially uniform lean air-fuel mixture is formed in and above the cavity 5a (FIG. 5 (III)). At this time, the combustible air-fuel mixture is supplied into the sub chamber 8 through the communication passage 9 by the compression of the piston 5.

  After that, late injection is performed in which the remaining fuel is injected into the cavity 5a in the middle to late stages of the compression stroke (FIG. 5 (III)). The fuel injected by the late injection collides with the cavity bottom 5b of the piston 5 and is guided from the cavity side wall 5c to the inner wall of the cylinder head and guided to the side of the sub chamber 8 before being guided to the sub chamber 8 side. It is ignited and burned by the substantially columnar jet flame released from the flame (Fig. 5 (IV)). Thus, the rich stratified mixture formed on the upper side of the cavity side wall 5c of the piston 5 is combusted by the substantially columnar jet flame from the sub chamber 8.

  6 shows the mixture behavior when a rich stratified mixture is formed in the cavity 5a and on the upper side in the cylinder axial direction of the side wall 5c in the high load region as shown in FIGS. ing. FIG. 6 shows each state from the compression bottom dead center (BDC) direction to the compression top dead center (TDC) direction and a state where the engine load has increased. That is, FIGS. 6A to 6C show a case where the operation condition is a middle load region from the compression bottom dead center direction to the compression top dead center direction, and FIGS. ) Shows the cases where the load increases in FIGS.

In this case, the fuel injection valve 6 injects a part of the total fuel injection amount at an early stage during the intake stroke to form a lean air-fuel mixture in the entire main combustion chamber 4 (FIG. 6 (a), ( a ′)).
Then, the remaining fuel is injected into the cavity 5a during the compression stroke (FIGS. 6B and 6B). In FIG. 6 (b ′), the fuel injection timing is retarded as the load increases in order to prevent the rich stratified mixture from moving from the upper side in the cylinder axial direction of the cavity side wall 5c to the sub chamber 8 side. .

  6 (c) and 6 (c '), the late-injected fuel collides with the cavity bottom 5b of the piston 5 to form a substantially hollow cylindrical rich mixture on the upper side from the cavity side wall 5c. In this case, a lean air-fuel mixture is formed in the entire main combustion chamber 4 by early injection in FIG. 6A as compared with the stratified air-fuel mixture at medium to high loads shown in FIG. When late injection is performed, a lean air-fuel mixture is distributed outside the cavity side wall 5c in the main combustion chamber 4. As a result, the fuel is completely burned in the entire main combustion chamber 4.

  According to the present embodiment, the fuel injection valve 6 that directly injects fuel into the combustion chamber 4 and the fuel ignition source (for example, a jet flame) are discharged into the combustion chamber 4 and injected from the fuel injection valve 6. In an internal combustion engine comprising an ignition device that ignites fuel, a lean stratified mixture is formed in the vicinity of the fuel ignition source discharge portion of the ignition device, and at a position away from the fuel ignition source discharge portion of the ignition device A rich stratified mixture is formed that is ignited by a fuel ignition source. For this reason, since a lean stratified mixture is formed in the vicinity of the fuel ignition source discharge part of the ignition device, it is possible to suppress the occurrence of abnormal rapid combustion and pre-ignition, and at a position away from the vicinity of the fuel ignition source discharge part Since the rich stratified mixture is ignited by the fuel ignition source released from the ignition device, stable operation can be performed even under operating conditions with a large amount of fuel injection.

Further, according to the present embodiment, the cavity 5a that receives the fuel injected from the fuel injection valve 6 is formed on the piston crown surface, and a rich stratified mixture is formed in and above the cavity 5a. For this reason, a rich stratified mixture can be stably formed at a predetermined position.
Further, according to the present embodiment, the side wall 5c is formed at the peripheral edge of the cavity 5a, and the rich stratified mixture formed on the upper side of the cavity 5a is formed on the upper side of the side wall 5c of the cavity 5a. Is done. For this reason, the fuel injected from the fuel injection valve 6 can be formed in the cylinder axial direction upper side by the side wall part 5c of the cavity 5a.

  Further, according to the present embodiment, the ignition device ignites the sub chamber 8 communicating with the combustion chamber 4 via the communication passage 9 and the gas in the sub chamber 8, so that the combustor 9 on the combustion chamber 4 side of the communication passage 9 is ignited. And ignition means for releasing the fuel ignition source into the combustion chamber 4 from the fuel ignition source discharge portion. For this reason, the ignition means can ignite the gas in the sub chamber 8 to release the fuel ignition source from the communication passage 9 into the main combustion chamber 4.

According to the present embodiment, the ignition means is the spark plug 7. For this reason, the gas in the sub chamber 8 can be easily ignited.
Further, according to the present embodiment, the rich stratified gas mixture and the lean stratified gas mixture are formed under predetermined operating conditions. For this reason, a rich stratified gas mixture and a lean stratified gas mixture can be appropriately formed according to the operating conditions.

Further, according to the present embodiment, the predetermined operation condition is from a medium load to a high load. For this reason, the driving | running | working at this driving | running load level can be performed, and abnormal rapid combustion and preignition can be suppressed. In addition, when no stratified mixture is formed below this operating load level, negative work due to pump loss is reduced at medium to high loads, so that unburned component emissions can also be reduced.
Further, according to the present embodiment, the fuel injection valve 6 performs early fuel injection from the latter half of the intake stroke to the middle of the compression stroke, and performs late fuel injection from the middle of the subsequent compression stroke to the latter half of the compression stroke. Therefore, a lean stratified mixture can be formed in the main combustion chamber 4 by early injection, and a rich stratified mixture is formed in the main combustion chamber 4 away from the fuel ignition source discharge portion of the ignition device by late injection. Can be formed.

Further, according to the present embodiment, the fuel injection valve 6 performs early injection of fuel during the intake stroke when the predetermined operating condition is a high load, and forms a lean air-fuel mixture throughout the main combustion chamber 4. For this reason, a stratified mixture can be formed in the entire main combustion chamber 4 and complete combustion can be performed in the entire main combustion chamber 4 when ignition is performed by the ignition device.
Further, according to the present embodiment, the fuel injection valve 6 performs the late injection of the fuel during the compression stroke. Therefore, a rich stratified mixture can be formed in the main combustion chamber 4 at a position away from the fuel ignition source discharge portion of the ignition means.

Further, according to the present embodiment, the fuel injection valve 6 advances the injection timing of the early injection as the load increases. For this reason, it can prevent that a rich stratified air-fuel mixture moves to the fuel ignition source discharge | release part of an ignition device.
Further, according to the present embodiment, the fuel injection valve 6 retards the injection timing of the late injection as the load increases. For this reason, the uniformity of the lean air-fuel mixture in the vicinity of the fuel ignition source discharge portion of the ignition device is increased, and combustion with relatively little NOx can be realized.

Next, a second embodiment of the present invention will be described.
The present embodiment performs control to form a lean stratified gas mixture and a rich stratified gas mixture as shown in FIGS. 3 (B) and (III) at the time of the catalyst temperature increase request, and is performed according to the flowchart of FIG. The
In step 1 (shown as “S1” in the figure, the same applies hereinafter), it is determined whether or not the temperature of the catalyst 13 is requested, that is, whether or not the catalyst 13 is activated. In this determination, for example, it is assumed that the catalyst temperature is detected by the temperature sensor 14 that detects the temperature of the catalyst 13, and the catalyst 13 is activated when the catalyst temperature is equal to or higher than a predetermined temperature. If the catalyst temperature sensor is not provided, the catalyst activity is judged based on the coolant temperature and the number of cycles after start-up, or the current catalyst temperature is estimated from the elapsed time of continuous operation in the low load region. The activity of the catalyst 13 is determined.

If it is determined in step 1 that the temperature of the catalyst 13 has been increased, that is, if it is determined that the catalyst 13 is in an inactive state, the process proceeds to step 2. On the other hand, if it is determined that the catalyst 13 is in an active state, the process proceeds to step 3.
In step 2, as the catalyst temperature increase request control, the fuel of the fuel injection valve 6 is formed so that a rich stratified mixture is formed on the upper side in the cylinder axial direction of the piston side wall portion 5c as shown in FIGS. While controlling the injection timing and the fuel injection amount, a substantially columnar jet flame (fuel ignition source) is formed in the main combustion chamber 4 from the communication passage 9 of the sub chamber 8 by ignition of the spark plug 7 in the sub chamber 8. Thus, combustion is performed in the main combustion chamber 4.

In the catalyst temperature increase request control, early injection in which a part of the total fuel injection amount is injected from the fuel injection valve 6 is performed early in the compression stroke in the middle to high load region.
As a result, the fuel injected between the latter half of the intake stroke and the middle half of the compression stroke (or the first half of the compression stroke) collides with the cavity bottom 5b, and from the cavity side wall 5c while entraining the surrounding air by the momentum of the spray. A substantially uniform stratified lean air-fuel mixture is formed in and above the cavity 5a by being guided upward in the direction (FIG. 5 (III)). In addition, a lean stratified mixture is formed in the vicinity of the fuel ignition source discharge part of the ignition device to suppress the occurrence of abnormal rapid combustion and pre-ignition, and in a position away from the vicinity of the fuel ignition source discharge part. Since a stratified mixture is formed and ignition is performed by the fuel ignition source released from the ignition device, stable operation can be performed even under operating conditions with a large amount of fuel injection.

Further, the injection timing of the early injection is advanced as the engine load increases in order to improve the uniformity of the lean air-fuel mixture in the vicinity of the communication passage 9 in the sub chamber 8 and realize combustion with less NOx. Thereafter, late injection of fuel is performed in the cavity 5a between the middle stage of the compression stroke and the latter stage of the compression stroke (FIG. 5 (III)).
Then, before the rich air-fuel mixture injected by the fuel injected in the late injection is guided from the cavity side wall portion 5c to the inner wall of the cylinder head and guided to the side of the sub chamber 8, it is substantially columnar from the communication passage 9 of the sub chamber 8. A jet flame is formed (FIG. 5D). As a result, the rich stratified mixture formed on the cylinder axial direction upper side of the cavity side wall portion 5c of the piston 5 is ignited by the substantially columnar jet flame from the sub chamber 8 and burned.

Further, outside the rich stratified mixture in a hollow cylindrical shape formed on the upper side of the cavity side wall portion 5c, the cylinder wall flow is reduced, so that the discharge of unburned HC is also reduced. Further, in order to reduce the combustion efficiency, the ignition timing is set to be retarded than during normal operation.
In step 3, the process shifts to normal control.
According to the present embodiment, the rich stratified air-fuel mixture and the lean stratified air-fuel mixture are formed when a temperature increase request is made for the exhaust purification catalyst 13 disposed in the exhaust passage 11 (step 1). For this reason, when the temperature of the catalyst 13 is required to be raised, combustion control is performed by increasing the exhaust gas temperature and discharging most of the injected fuel into the exhaust passage 11 as unburned components such as HC and CO to reduce the combustion efficiency. However, in this case, since the total fuel injection amount increases relative to the normal operation even when the engine is under a low load, the main combustion chamber 4 is separated from the entire fuel combustion source, that is, the fuel ignition source discharge portion of the ignition device. Although the concentration of the air-fuel mixture at the position becomes relatively rich, in this configuration, it is possible to suppress the occurrence of abnormal rapid combustion and preignition associated therewith.

The block diagram of the internal combustion engine in the 1st Embodiment of this invention Diagram showing a state where a substantially columnar fuel ignition source is formed in the main combustion chamber Diagram showing mixture distribution with respect to engine load Equivalent ratio of mixture to engine load Diagram showing formation behavior of rich stratified mixture in medium to high load range Diagram showing the formation behavior of a rich stratified mixture in a high-load region Control flow to form lean stratified mixture and rich mixture

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 4 Main combustion chamber 5 Piston 5a Cavity 5b Bottom 5c Side wall 6 Fuel injection valve 7 Spark plug 8 Sub chamber 9 Communication path 13 Catalyst 14 Temperature sensor 17 Fuel pump 20 ECU

Claims (8)

A cavity provided in the piston crown surface;
A fuel injection valve that is disposed substantially in the center of the combustion chamber and directly injects fuel into the combustion chamber;
A sub-chamber ignition device that is disposed in the vicinity of the fuel injection valve, emits a flame serving as a fuel ignition source into the combustion chamber through the communication passage, and ignites the air-fuel mixture in the combustion chamber ;
A control unit for controlling the injection timing of the fuel injection valve and the ignition timing of the ignition device;
An internal combustion engine comprising:
In the middle and high load range of the engine, split injection of early injection and late injection is performed from the fuel injection valve, and the early injection forms a lean air-fuel mixture in the cavity and above or in the entire combustion chamber, It is configured to form a locally rich air-fuel mixture that rises cylindrically upward along the side wall of the cavity by the late injection that is injected toward the cavity,
Further, the communication path of the ignition device is disposed on the inner peripheral side of the cavity in plan view, and before the locally rich air-fuel mixture formed by the late injection reaches the communication path of the ignition device An internal combustion engine that performs ignition by the ignition device . The ignition device is
A sub-chamber which communicates through said communication passage and said combustion chamber,
And ignition means you point the fire in the sub-chamber of a gas,
The internal combustion engine according to claim 1, comprising: The internal combustion engine according to claim 2, wherein the ignition means is a spark plug. The fuel injection valve performs early injection of fuel from the late stage of the intake stroke to the middle stage of the compression stroke, and performs late injection of the fuel from the middle stage of the subsequent compression stroke to the late stage of the compression stroke . 4. The internal combustion engine according to any one of 3 . 4. The fuel injection valve according to claim 1, wherein the fuel injection valve performs early fuel injection during an intake stroke in a high load region of the engine to form a lean air-fuel mixture in the entire combustion chamber. The internal combustion engine described. The internal combustion engine according to claim 5 , wherein the fuel injection valve performs late injection of fuel during a compression stroke. The internal combustion engine according to any one of claims 1 to 6, wherein the fuel injection valve advances the injection timing of the early injection as the load increases. The fuel injection valve, with increasing load, the internal combustion engine according to claim 1, characterized in that retarding the injection timing of the later injection.

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