JP2016089747A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the stability of diesel combustion, in an internal combustion engine which performs the diesel combustion by using fuel which is relatively high in a self-ignition temperature like gasoline.SOLUTION: An internal combustion engine generates the self-ignition and the dispersion combustion of fuel by performing first injection at first injection timing during a compression stroke, generating pre-combustion by igniting a fuel spay by a first ignition device, and starting the execution of second injection at timing after the ignition by the first ignition device, and before a compression stroke top dead point that is second injection timing which is set as timing at which the combustion of injection fuel is started with a flame generated by the pre-combustion as a starting point. A second ignition device is installed within a prescribed range which is regulated by an angle smaller than 180 degrees in a rotation direction of a swirl flow with the first ignition device as a starting point. Then, when generating the pre-combustion, the ignition by the second ignition device is performed after the ignition by the first ignition device, and before the second ignition timing.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a control device for an internal combustion engine.

  So-called diesel combustion, which is a combustion mode in which fuel is directly injected into compressed air in the combustion chamber and self-ignited and diffusely combusted, has higher thermal efficiency than combustion by spark ignition. In recent years, in order to enjoy such advantages of diesel combustion even in a gasoline engine, a technology for establishing combustion by self-ignition and diffusion combustion of gasoline has been developed.

  For example, Patent Literature 1 discloses a technique for realizing diesel combustion using natural gas or the like having a relatively high self-ignition temperature as a fuel. In the technique disclosed in Patent Document 2, first, an air-fuel mixture capable of spark ignition is formed by performing fuel injection in a predetermined spark ignition region in the combustion chamber in the initial stage or middle stage of the compression stroke. Then, spark ignition combustion is performed by igniting the air-fuel mixture formed in the spark ignition region at a time immediately before the top dead center of the compression stroke. As a result, the combustion chamber is brought into a high temperature and high pressure state capable of self-ignition of natural gas. Thereafter, the fuel is directly injected into the combustion chamber in a high-temperature and high-pressure state, and the fuel is diesel-combusted.

  Patent Document 2 discloses a configuration in which a main spark plug and an auxiliary spark plug are installed in a gasoline engine that burns premixed gas in a cylinder by self-ignition in a predetermined operating region. In this Patent Document 2, when the occurrence of knocking is detected when the engine is outside the operating range for self-igniting the premixed gas, auxiliary ignition is performed on the advance side of the ignition to the premixed gas by the main spark plug. A technique for performing auxiliary ignition with a plug is also disclosed.

JP 2003-254105 A JP 2004-285925 A

  An object of the present invention is to improve the stability of diesel combustion in an internal combustion engine that performs diesel combustion using a fuel having a relatively high self-ignition temperature such as gasoline.

An internal combustion engine control device according to the present invention is a control device for an internal combustion engine in which a swirl flow that is a swirling flow around a cylinder central axis is generated in a combustion chamber, and has a plurality of nozzle holes, and the cylinder center in the combustion chamber A fuel injection valve for injecting fuel from the vicinity of the shaft toward the cylinder wall surface, and the fuel injection valve so that the spray injected from the fuel injection valve passes through the ignitable region and can be directly ignited The first ignition device with the relative position determined, and the first ignition by the fuel injection valve at the first injection timing during the compression stroke and the first ignition with respect to the pre-spray formed by the first injection A pre-combustion unit that performs pre-combustion to burn a part of the fuel injected by the first injection by igniting by the device, and after the ignition to the pre-spray by the first ignition device and on the compression stroke death A second injection timing which is a predetermined injection interval that is set to start combustion of the injected fuel starting from the flame generated by the pre-combustion, which is the previous time. And a main combustion section for performing main combustion for causing the fuel to self-ignite and diffusing and burning at least a portion of the fuel injected by the second injection. In the control device for an internal combustion engine, the fuel of the fuel injection valve in the combustion chamber is within a predetermined region defined by an angle of less than 180 degrees in the rotational direction of the swirl flow starting from the first ignition device. A second ignition device installed at a position where the distance from the injection position is larger than that of the first ignition device, wherein the pre-combustion unit performs the pre-combustion; In this case, ignition by the second ignition device is executed at a predetermined second ignition timing after the first ignition timing that is the ignition timing in the first ignition device and before the second injection timing. To do.

  According to the present invention, it is possible to improve the ignitability of pre-spraying when performing pre-combustion. As a result, the stability of diesel combustion can be improved.

It is a figure which shows schematic structure of the internal combustion engine with which the Example of this invention is applied, its intake system, and an exhaust system. FIG. 2 is a first view showing an arrangement of a first spark plug and a second spark plug in the internal combustion engine shown in FIG. 1. FIG. 3 is a second view showing the arrangement of the first spark plug and the second spark plug in the internal combustion engine shown in FIG. 1. It is a figure for demonstrating the basic combustion control performed in the Example of this invention. It is a figure which shows transition of the heat release rate in a combustion chamber when the basic combustion control which concerns on the Example of this invention is performed. It is a figure which shows the change of transition of the heat release rate in a combustion chamber when the ratio of the 1st injection fuel quantity and the 2nd injection fuel quantity is changed in the basic combustion control which concerns on the Example of this invention. It is a figure which shows the time correlation of the 1st injection regarding the low load combustion control which concerns on the Example of this invention, 2nd injection, and ignition. It is a flowchart which shows the flow of the combustion control which concerns on the Example of this invention. The engine load of the internal combustion engine 1, the ignition timing by the first spark plug and the second spark plug, the first injected fuel amount, and the unburned ratio of the first injected fuel when performing pre-combustion according to the reference example of the present invention FIG.

[Example]
Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its intake / exhaust system. An internal combustion engine 1 shown in FIG. 1 is a 4-stroke cycle spark ignition internal combustion engine (gasoline engine) having a plurality of cylinders. Further, the internal combustion engine 1 is configured such that a swirl flow that is a swirl flow around the central axis of the cylinder 2 is generated in the combustion chamber of each cylinder 2. However, it is not necessary that the center axis of the cylinder 2 and the center axis of the swirl flow exactly coincide with each other. In FIG. 1, only one cylinder among a plurality of cylinders is shown.

  Each cylinder 2 of the internal combustion engine 1 is internally slidably provided with a piston 3. The piston 3 is connected to an output shaft (crankshaft) (not shown) via a connecting rod 4. Further, the inside of the cylinder 2 communicates with the intake port 7 and the exhaust port 8. The opening end of the intake port 7 in the cylinder 2 is opened and closed by an intake valve 9. The open end of the exhaust port 8 in the cylinder 2 is opened and closed by an exhaust valve 10. The intake valve 9 and the exhaust valve 10 are each opened and closed by an intake cam and an exhaust cam (not shown).

  Each cylinder 2 is provided with a fuel injection valve 6 for injecting fuel into the cylinder in the vicinity of the central top of the combustion chamber formed in the cylinder 2. Further, each cylinder 2 is provided with a first spark plug 51 and a second spark plug 52 that can ignite the fuel injected from the fuel injection valve 6. 2 and 3 are views showing the installation positions of the first spark plug 51 and the second spark plug 52 according to the present embodiment. As shown in FIG. 2, the first spark plug 51 is provided between the opening of the intake port 7 and the opening of the exhaust port 8. The second spark plug 52 has a region α (region shown by hatching in FIG. 2) defined by an angle of less than 180 degrees in the swirl flow rotation direction (clockwise direction in FIG. 2) starting from the first spark plug 51. Is provided inside. Specifically, the second spark plug 52 is disposed between the openings of the two exhaust ports 8. Further, the distance L2 from the fuel injection position of the fuel injection valve 6 to the second spark plug 52 is larger than the distance L1 from the fuel injection position of the fuel injection valve 6 to the first spark plug 51.

  FIG. 3 shows the positional relationship between the fuel spray injected from the fuel injection valve 6 and the two spark plugs 51 and 52. As shown in FIG. 3, the fuel injection valve 6 has injection holes 6a so as to be able to inject fuel in 16 directions substantially radially from the vicinity of the central axis of the combustion chamber toward the cylinder wall surface. Then, at least one of the fuel sprays injected from the injection holes 6a passes through the regions 51a and 52a between the electrodes, which are the ignitable regions of the first spark plug 51 and the second spark plug 52. The relative positions of the first spark plug 51 and the second spark plug 52 with respect to the fuel injection valve 6 are determined. As a result, the spray that has passed through the region 51 a can be directly ignited by a spark generated between the electrodes of the first spark plug 51. Further, the spray that has passed through the region 52 a can be directly ignited by a spark generated between the electrodes of the second spark plug 52.

  In addition, the installation position of the 1st ignition device which concerns on this invention is not restricted between the opening part of an intake port, and the opening part of an exhaust port. Moreover, the installation position of the 2nd ignition device which concerns on this invention is not restricted between the opening parts of two exhaust ports. In the present invention, the second spark plug needs to be provided in a region defined by an angle of less than 180 degrees in the swirl flow rotation direction starting from the first spark plug. It is not always necessary for the fuel spray to pass through the ignitable region of the second spark plug.

  The first spark plug 51, the second spark plug 52 and the fuel injection valve 6 configured as described above enable spray guide combustion. That is, the first spark plug 51 and the second spark plug 52 which are arranged so that the fuel injected from the fuel injection valve 6 can be directly ignited, and the fuel injection valve 6 open the intake valve 9 of the internal combustion engine 1. It is possible to ignite the injected fuel passing through the region 51a or 52a at any time regardless of the valve timing or the position of the piston 3. Conventionally, air guide combustion and wall guide combustion are known as other combustion methods in which the fuel injected from the fuel injection valve is directly ignited by an ignition plug. In the air guide combustion, the fuel injected from the fuel injection valve is carried in the vicinity of the spark plug by the air flow flowing into the combustion chamber by opening the intake valve, and ignited by the spark plug. In the wall guide combustion, the injected fuel is carried to the vicinity of the spark plug using the shape of the cavity formed at the top of the piston and ignited by the spark plug. However, in these air guide combustion and wall guide combustion, it is difficult to perform fuel injection and ignition unless the opening timing of the intake valve and the piston position are in a predetermined state. Therefore, the spray guide combustion according to the present embodiment enables fuel injection and ignition timing control with a very high degree of freedom as compared with these air guide combustion and wall guide combustion.

Returning to FIG. 1, the intake port 7 communicates with the intake passage 70. A throttle valve 71 is disposed in the intake passage 70. An air flow meter 72 is disposed in the intake passage 70 upstream of the throttle valve 71. On the other hand, the exhaust port 8 communicates with the exhaust passage 80. An exhaust purification catalyst 81 for purifying the exhaust discharged from the internal combustion engine 1 is disposed in the exhaust passage 80. As will be described later, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 is a lean air-fuel ratio that is higher than the stoichiometric air-fuel ratio. Therefore, as the exhaust purification catalyst 81, a selective reduction type NOx catalyst capable of purifying NOx in the lean air-fuel ratio exhaust or a filter capable of collecting particulate matter (PM) in the exhaust can be employed.

  The internal combustion engine 1 is also provided with an electronic control unit (ECU) 20. The ECU 20 is a unit that controls the operating state of the internal combustion engine 1, an exhaust purification device, and the like. The ECU 20 is electrically connected to the air flow meter 72, the crank position sensor 21, and the accelerator position sensor 22 described above, and detection values of the sensors are input to the ECU 20. Therefore, the ECU 20 is an internal combustion engine 1 such as an intake air amount detected by the air flow meter 72, an engine rotational speed calculated based on a detected value of the crank position sensor 21, and an engine load based on a detected value of the accelerator position sensor 22. It is possible to grasp the operating state of Further, the fuel injection valve 6, the first spark plug 51, the second spark plug 52, the throttle valve 71, and the like are electrically connected to the ECU 20, and these elements are controlled by the ECU 20.

<Basic combustion control>
The basic combustion control, which is the basic combustion control executed in the internal combustion engine 1 configured as described above, will be described with reference to FIG. FIG. 4 shows the flow of fuel injection and ignition related to combustion control performed in the internal combustion engine 1 (see the upper part of FIG. 4A) and the combustion by the fuel injection and ignition in the time series progressing from the left side to the right side of the figure. FIG. 5 schematically shows a transition of an event related to combustion assumed to occur in a chamber (see the lower part of FIG. 4A). FIG. 4B shows a temporal correlation between the first injection and the second injection, which are the fuel injections shown in FIG. 4A, and ignition. It should be noted that the form shown in FIG. 4 is schematically shown only for explaining the basic combustion control according to the present embodiment, and the present invention should not be interpreted as being limited to this form. is not.

  In the basic combustion control according to the present embodiment, the first injection and the second injection are executed by the fuel injection valve 6 in one combustion cycle. The first injection is a fuel injection executed during the compression stroke. The second injection is a fuel injection that starts after the first injection and before the compression stroke top dead center (TDC). The execution of the second injection is started at a time before the TDC, but the execution may be continued until after the TDC. As shown in FIG. 4B, the injection start timing of the first injection (hereinafter simply referred to as “first injection timing”) is Tp, and the injection start timing of the second injection (hereinafter simply “second”). Tm is referred to as “injection timing”. Further, an interval (Tm−Tp) between the first injection timing and the second injection timing is defined as a first injection interval Di1. Further, the combustion by the first injection is executed as the spray guide combustion described above. Spray guide combustion in the first injection in the basic combustion control is performed by ignition by the first spark plug 51. That is, the first spark plug 51 ignites the pre-spray formed by the fuel injected by the first injection (hereinafter referred to as “first injected fuel”). The ignition timing of the first spark plug 51 in this basic combustion control is referred to as “first ignition timing”. This first ignition timing is defined as Ts1 as shown in FIG. 3B, and an interval (Ts1-Tp) from the start of execution of the first injection to the first ignition timing is defined as a first ignition interval Ds1. .

Next, the flow of basic combustion control according to the present invention will be described.
(1) First Injection In the basic combustion control, firstly, during one combustion cycle, first injection is performed at the first injection timing Tp during the compression stroke. The first injection timing Tp is determined based on the correlation with the second injection timing Tm described later. By performing the first injection, as shown in FIG. 3, the pre-spray of the first injected fuel injected from the fuel injection valve 6 passes through the ignitable region 51 a of the first spark plug 51 in the combustion chamber. . Immediately after the execution of the first injection is started in this way, the pre-spray of the first injected fuel does not diffuse widely in the combustion chamber, and the surrounding air is engulfed at the tip by the penetration force of the spray. Proceed through the combustion chamber. Therefore, a stratified mixture is formed in the combustion chamber by pre-spraying the first injected fuel.

(2) Ignition to the first injected fuel The first ignition timing at which a predetermined first ignition interval Ds1 has elapsed from the first injection timing with respect to the pre-spraying of the first injected fuel stratified as described above At Ts1, ignition by the first spark plug 51 is performed. As described above, since the first injected fuel is stratified, the local air-fuel ratio around the first spark plug 51 is an empty space that can be combusted by the ignition even if the amount of the first injected fuel is small. The fuel ratio is set. By this ignition, spray guide combustion with the first injected fuel is performed. In other words, the first ignition interval Ds1 is set so that spray guide combustion is possible. In addition to the pressure increase due to the compression action of the piston 3, this spray guide combustion is performed, whereby a further temperature increase in the combustion chamber is obtained. However, of the first injected fuel, a part of the fuel burned by the spray guide combustion is a part, and most of the fuel is not used for the combustion by the ignition of the first spark plug 51 and after the ignition, the “unburned fuel” ”In the combustion chamber. This is because, in the stratified mixture formed by the first injected fuel, in a portion relatively distant from the electrodes of the first spark plug 51, the air cannot be propagated because the air-fuel ratio is high. However, the unburned fuel is exposed to a high temperature atmosphere by burning a part of the first injected fuel in the combustion chamber. Therefore, it is expected that at least a part of the unburned fuel is in a state of being reformed to a physical property with improved combustibility by a low-temperature oxidation reaction under a situation where combustion does not occur.

(3) Second Injection Next, the second injection timing Tm before the compression stroke top dead center where a predetermined first injection interval Di1 has elapsed from the first injection timing (from the first ignition timing Ts1 to Di by the first ignition plug 51). The execution of the second injection by the fuel injection valve 6 is started at the time Tm) when the time of -Ds1 has elapsed. In the internal combustion engine 1, as will be described later, the second injected fuel is subjected to self-ignition and diffusion combustion and contributes to the engine output. Therefore, the second injection timing Tm is set to a timing (hereinafter referred to as “appropriate injection timing”) at which the engine output obtained by the combustion of the second injected fuel in an amount determined by the engine load or the like is approximately maximum. However, the combustion of the second injected fuel is started using the flame generated by the ignition of the pre-spray of the first injected fuel as a fire type. That is, the second injection timing Tm is set to an appropriate injection timing, and the first injection interval Di1 is set so that the combustion of the second injected fuel is started from the flame generated by the ignition of the pre-spray. Yes. By setting the second injection timing Tm and the first injection interval Di1 in this way, the first injection timing Tp is inevitably determined. When the combustion of the second injected fuel is started, the temperature in the combustion chamber further increases. As a result, the unburned residue of the first injected fuel and the second injected fuel are self-ignited in the temperature rising field, and these fuels are subjected to diffusion combustion. At this time, when the unburned combustibility of the first injected fuel is enhanced as described above, it is expected that the self-ignition of the fuel after the start of the second injection is further promoted.

Thus, in the basic combustion control according to the present embodiment, the series of combustion as described above is performed by the first injection, the ignition, and the second injection. In the present specification, the combustion start of the second injected fuel starting from the flame generated by the ignition of the pre-spray of the first injected fuel in this way, and the unburned fuel and the first of the subsequent first injected fuel are started. The correlation between the first injection and the second injection that enables self-ignition and diffusion combustion with the two-injected fuel is referred to as “first-second injection correlation”. That is, in the basic combustion control according to the present embodiment, the second injection having the first and second injection correlations is performed with respect to the first injection and the ignition for the first injected fuel.

  Here, FIG. 5 shows the transition of the heat generation rate in the combustion chamber when the basic combustion control according to the present embodiment is performed. FIG. 5 shows the transition of the heat generation rate corresponding to the four different control modes L1 to L4 when the engine speed of the internal combustion engine 1 is 2000 rpm. In these control forms L1 to L4, the first injection timing Tp, the first injected fuel amount (that is, the execution period of the first injection), the second injection timing Tm, and the ignition timing Ts are the same. The two-injected fuel amount (that is, the execution period of the second injection) is different for each control mode. That is, the second injected fuel amount is L1> L2> L3> L4. That is, FIG. 4 shows a change in transition of the heat generation rate according to increase / decrease of the second injected fuel amount on the precondition that the same first-second injection correlation is established. Will be.

  Here, in FIG. 5, the primary peak of the heat generation rate appears in the portion Z1 surrounded by a dotted line. This primary peak indicates the heat generated by burning the first injected fuel by ignition (that is, heat generated by spray guide combustion). At the time when the primary peak of the heat generation rate appears, the second injection has not yet been performed, and the flame generated by ignition of the first injected fuel in the combustion chamber and the first injection not combusted by the ignition There is unburned fuel that is the fuel.

  Then, the execution of the second injection is started at a time Tm after the time when the primary peak of the heat generation rate occurs and before the compression stroke top dead center. At this time, as described above, the second injected fuel starts to burn using the flame generated by the ignition of the pre-spray of the first injected fuel as a fire type, and then self-ignites with the unburned residue of the first injected fuel. Further, it is subjected to diffusion combustion. As a result, a secondary peak that is the maximum peak of the heat generation rate occurs at the time when the top dead center of the compression stroke has passed. Here, in FIG. 5, as the second injected fuel amount increases (that is, as the second injection period becomes longer), the value of the secondary peak of the heat generation rate increases and the generation of the secondary peak occurs. The time is late. This means that the combustion period of the second injected fuel becomes longer as the amount of the second injected fuel increases. From this, it can be inferred that the unburned residue of the second injected fuel and the first injected fuel is subjected to diffusion combustion or combustion that can be substantially equated with diffusion combustion.

  Furthermore, the self-ignition of fuel generated in the basic combustion control according to the present embodiment will be described based on FIG. FIG. 6 shows the first injection fuel amount and the first injection amount while keeping the total injection amount (total of the first injection fuel amount and the second injection fuel amount) in one combustion cycle in the basic combustion control according to the present embodiment. The transition of the heat generation ratio in the combustion chamber of each of the two forms L8 and L9 in which the ratio with the two injected fuel amounts is changed is shown. In FIG. 6, the engine speed of the internal combustion engine 1 is 2000 rpm. Further, the ratio of the first injected fuel amount is higher in the L9 form than in the L8 form. In other words, the L9 form has a larger amount of the first injected fuel than the L8 form, and as a result, the unburned amount of the first injected fuel has also increased. In this case, as shown in FIG. 6, in the form of L9, the secondary peak value of the heat generation rate after the top dead center of the compression stroke is larger than in the form of L8. Furthermore, in the form of L9, the falling speed from the secondary peak value of the heat generation rate (the slope of the graph after the secondary peak) is larger than in the form of L8. In the combustion of the unburned first injected fuel after the start of the second injection and the combustion of the second injected fuel, the combustion by self-ignition is further promoted in the form of L9 than in the form of L8 (that is, The ratio of the fuel combusted by self-ignition is high, and the ratio of the fuel combusted by diffusion combustion is low. From this, it is considered that the unburned residue of the first injected fuel contributes to the promotion of self-ignition of the fuel after the second injection.

As described above, in the basic combustion control according to this embodiment, the first injection and the first spark plug 5
The second injection is executed after the spray guide combustion by the ignition at 1, thereby causing the self-ignition and diffusion combustion of the fuel. Therefore, it is considered that the combustion by the basic combustion control is similar to so-called diesel combustion or can be substantially identified. Therefore, the air-fuel ratio of the air-fuel mixture in the combustion chamber can be set to an extremely high lean air-fuel ratio (about 20 to 70). Further, in order to realize combustion at such a lean air-fuel ratio, in the combustion control according to the present embodiment, the opening degree of the throttle valve 71 is made larger than that in the conventional gasoline engine combustion control (homogeneous stoichiometric control). . Therefore, the pump loss in the internal combustion engine 1 can be reduced. Furthermore, since the combustion contributing to the engine output is performed by self-ignition and diffusion combustion, the cooling loss in the internal combustion engine 1 can also be reduced as compared with the conventional homogeneous stoichiometric control. Therefore, according to the basic combustion control according to the present embodiment, it is possible to achieve high thermal efficiency that cannot be realized by conventional combustion control of a gasoline engine.

  Further, as described above, the second injection timing is set to an appropriate injection timing at which the engine output of the internal combustion engine 1 is substantially maximized. Therefore, it is possible to cope with an increase in engine load to some extent by increasing the second injected fuel amount. However, since the second injection is performed when the pressure in the combustion chamber near the top dead center of the compression stroke is very high, the penetration of the fuel spray injected from the fuel injection valve 6 is reduced. That is, the fuel spray injected by the second injection is difficult to diffuse over a wide range. Therefore, when the amount of the second injected fuel is excessively increased, the oxygen present around the spray of the second injected fuel, that is, the amount of oxygen provided for the combustion of the second injected fuel is insufficient with respect to the fuel. As a result, the amount of smoke generated may increase. Further, in the basic combustion control according to the present embodiment, it is necessary to cause the self-ignition of the fuel after the second injection. However, if the amount of the second injected fuel is excessively increased, the combustion chamber is caused by the latent heat of vaporization of the second injected fuel. There is also a risk that the temperature of the fuel will decrease and combustion may become unstable.

  On the other hand, the first injection is performed at the first injection timing Tp during the compression stroke. Therefore, it is considered that when the first injected fuel is burned by ignition by the first spark plug 51, it acts to hinder the engine output of the internal combustion engine 1. However, in the combustion by the ignition of the first sprayed fuel to the pre-spray, it is only necessary to form a flame that becomes a fire type for the combustion of the second injected fuel. Therefore, as described above, only a part of the first injected fuel is subjected to combustion by ignition. Therefore, the effect | action which prevents the engine output by the spray guide combustion of the said 1st injection fuel is small. The unburned unburned portion of the first injected fuel that is not used for spray guide combustion is used for self-ignition and diffusion combustion together with the second injected fuel after the second injection, thereby contributing to the engine output. Therefore, it is possible to cope with an increase in the engine load by increasing the first injected fuel amount and increasing the unburned fuel ratio.

  Further, at the second injection timing, the unburned residue of the first injected fuel is diffused in a wider range than the fuel spray of the second injected fuel in the combustion chamber. Therefore, when the unburned residue of the first injected fuel is subjected to self-ignition and diffusion combustion, it is easy to ensure sufficient oxygen. Therefore, when the increase in the first injected fuel and the increase in the unburned ratio correspond to the increase in engine load, the amount of smoke generated can be suppressed as compared with the case where the second injected fuel amount is increased.

<Low load combustion control>
Next, in the present embodiment, low load combustion control that is executed in a low load region that is an operation region in which the engine load of the internal combustion engine 1 is equal to or less than a predetermined load will be described based on FIG. FIG. 7 is a diagram showing temporal correlations of the first injection, the second injection, the first ignition, and the second ignition related to the low load combustion control performed in the internal combustion engine 1 in the time series progressing from the left side to the right side of the drawing. is there.

In the low load region, the total fuel injection amount during one combustion cycle is a relatively small amount, and therefore the first injected fuel amount inevitably decreases. Therefore, when the first injection is executed, the amount of fuel passing through the ignitable region 51a of the first spark plug 51 is reduced. As a result, the first
When ignition is performed by the spark plug 51, pre-spray ignition is less likely to occur. That is, even in the low load region, if the basic combustion control as described above is executed in the same manner as in the high load region where the engine load of the internal combustion engine 1 is higher than the predetermined load, there is a risk that the ignitability of the pre-spray will be reduced. is there. And if the ignition of pre-spray does not occur, the fire type for burning the second injected fuel will not be formed. Therefore, when the ignitability of pre-spraying is lowered, the stability of diesel combustion is lowered.

  Therefore, in the present embodiment, when pre-combustion is performed in the low load region, the second ignition is performed in addition to the ignition to the pre-spray by the first spark plug 51 (hereinafter sometimes referred to as “first ignition”). Low-load combustion control for executing the second ignition by the plug 52 is performed. In FIG. 7, “second ignition timing” that is the ignition timing of the second ignition is Ts2. As shown in FIG. 7, the second ignition timing Ts2 is set to a predetermined timing after the first ignition timing Ts1 and before the second injection timing Tm.

  Here, in the internal combustion engine 1 according to the present embodiment, as described above, a swirl flow is generated in the combustion chamber. Therefore, the pre-spray that has passed through the ignitable region 51a of the first spark plug 51 but did not ignite by the ignition by the first spark plug 51 (hereinafter referred to as “pre-ignition pre-spray”) is the flow direction of the swirl flow (Clockwise direction in FIG. 2). Further, the kinetic energy of the pre-spray itself injected from the fuel injection valve 6 acts in a direction from the cylinder central axis side to the cylinder wall surface side. Accordingly, the pre-ignition pre-spray flows in the direction of the swirl flow and moves in the direction of the cylinder wall surface (that is, the direction away from the fuel injection position of the fuel injection valve 6). On the other hand, as described above, the second spark plug 52 has the two exhaust ports 8 at positions in the region α defined by an angle of less than 180 degrees in the rotational direction of the swirl flow with the first spark plug 51 as a starting point. Between the openings. Furthermore, the distance L2 from the fuel injection position of the fuel injection valve 6 to the second spark plug 52 is greater than the distance L1 from the fuel injection position of the fuel injection valve 6 to the first spark plug 51. In other words, the second spark plug 52 is located in the direction in which the pre-spraying after ignition proceeds. And the pre-spray after ignition is higher than the temperature of the pre-spray before the first ignition due to the ignition by the first spark plug 51 without ignition. That is, the pre-ignition pre-spray is more easily ignited by ignition than the pre-spray before the first ignition. Therefore, when the second ignition is performed by the second ignition plug 52 at the second ignition timing Ts2, there is a high possibility that the pre-spray after ignition is ignited. Therefore, the ignitability in the pre-combustion can be improved by performing the second ignition in addition to the first ignition. As a result, since the fire type for burning the second injected fuel is formed with a higher probability, the stability of diesel combustion can be improved.

  In order to ignite the pre-ignition pre-spray by the second ignition by the second ignition plug 52, the second ignition may be performed at a timing at which the post-ignition pre-spray is positioned in the ignitable region 52a of the second ignition plug 52. preferable. Therefore, in the low load combustion control according to the present embodiment, the interval (Ts2-Ts1) between the first ignition timing Ts1 and the second ignition timing Ts2 is determined so that the pre-spray after ignition starts from the ignitable region 51a of the first ignition plug 51. The second ignition timing Ts2 is determined so as to be a predetermined second ignition interval Ds2 that is a period until reaching the ignitable region 52a of the second spark plug 52. Here, the second ignition interval Ds2 defined by the crank angle is an angle formed by the ignitable region 51a of the first spark plug 51 and the ignitable region 52a of the second spark plug 52 in the rotational direction of the swirl flow, and It can be determined based on the swirl ratio of the swirl flow generated in the combustion chamber of the cylinder 2. That is, the second ignition interval Ds2 is a constant value regardless of the engine load and engine speed of the internal combustion engine 1.

<Combustion control flow>
Here, the control flow of the combustion control according to the present embodiment will be described with reference to FIG. FIG.
These are flowcharts which show the control flow of the combustion control which concerns on a present Example. This control flow is stored in advance in the ECU 20, and is repeatedly executed at predetermined intervals by executing a control program stored in the ECU 20 while the internal combustion engine 1 is operating.

  In this flow, first, in S101, the engine load Qe of the internal combustion engine 1 is calculated based on the detection value of the accelerator position sensor 22. Next, in S102, it is determined whether or not the engine load Qe calculated in S101 is higher than a predetermined load Qe0. The predetermined load Qe0 is a threshold value for distinguishing the low load region and the high load region. The predetermined load Qe0 is determined in advance based on experiments or the like and is stored in the ECU 20. If an affirmative determination is made in S102, that is, if the engine load of the internal combustion engine 1 belongs to the high load region, the process of S103 is then executed.

  In S103, the first injection fuel amount Sp, the second injection fuel amount Sm, the first injection timing Tp, the second injection timing Tm, and the ignition timing Ts for realizing basic combustion control are calculated in S101. It is determined based on the load Qe. The relationship between the first injected fuel amount Sp, the second injected fuel amount Sm, the first injection timing Tp, the second injection timing Tm, the ignition timing Ts, and the engine load Qe is such that the above-described first to second injection correlations. The relationship that can be established is predetermined based on experiments or the like. These relationships are stored in the ECU 20 as a map. In the map, when the first injected fuel amount Sp is increased as the engine load Qe increases, the first injection timing Tp and the ignition timing Ts are advanced according to the increased amount. When the first injection timing Tp is advanced, the first injection is executed with the pressure in the cylinder 2 being lower. That is, as the first injection timing Tp is advanced, the pre-spray penetration of the first injected fuel becomes relatively large. As a result, the amount of fuel that remains unburned without propagation of the flame generated by the ignition by the first spark plug 51 increases. Therefore, when the first injected fuel amount Sp is increased, the unburned rate of the first injected fuel can be increased by advancing the first injection timing Tp and the ignition timing Ts according to the increased amounts. In S103, the first injected fuel amount Sp, the second injected fuel amount Sm, the first injection timing Tp, the second injection timing Tm, and the ignition timing Ts are determined using the map.

  Next, in S104, the first fuel injection valve 6 performs the first injection fuel amount Sp, the second injection fuel amount Sm, the first injection timing Tp, the second injection timing Tm, and the ignition timing Ts determined in S103. Injection, second injection, and ignition by the first spark plug 51 are executed. Thereby, the basic combustion control according to the present embodiment is realized.

  On the other hand, when a negative determination is made in S102, that is, when the engine load of the internal combustion engine 1 belongs to the low load region, the process of S105 is executed next. In S105, the first injected fuel amount Sp, the second injected fuel amount Sm, the first injection timing Tp, the second injection timing Tm, the first ignition timing Ts1, and the second ignition timing for realizing the low load combustion control. Ts2 is determined based on the engine load Qe calculated in S101. Here, the relationship between the first injected fuel amount Sp, the second injected fuel amount Sm, the first injection timing Tp, the second injection timing Tm, the first ignition timing Ts1, and the engine load Qe is the case of the basic combustion control. In the same manner as described above, the relationship in which the first-second injection correlation described above can be established is determined in advance based on experiments or the like. The second ignition timing Ts2 is determined in advance so that the interval from the first ignition timing Ts1 is the above-described second ignition interval Ds2. In such low load combustion control, the first injected fuel amount Sp, the second injected fuel amount Sm, the first injection timing Tp, the second injection timing Tm, the first ignition timing Ts1, the second ignition timing Ts2, and the engine load The relationship with Qe is also stored in the ECU 20 as a map. In S105, the first injection fuel amount Sp, the second injection fuel amount Sm, the first injection timing Tp, the second injection timing Tm, the first ignition timing Ts1, and the second ignition timing Ts2 are determined using the map. Is done.

  Next, in S106, according to the first injected fuel amount Sp, the second injected fuel amount Sm, the first injection timing Tp, the second injection timing Tm, the first ignition timing Ts1, and the second ignition timing Ts2 determined in S105. The first and second injections by the fuel injection valve 6, the first ignition by the first spark plug 51, and the second ignition by the second spark plug 52 are executed. Thereby, the low load combustion control according to the present embodiment is realized.

<Modification>
When performing the pre-combustion, the operation region of the internal combustion engine 1 that executes the second ignition by the second ignition plug 52 in addition to the first ignition by the first ignition plug 51 is not necessarily limited to the low load region. . That is, even when the engine load of the internal combustion engine 1 belongs to the high load region, when performing pre-combustion, in addition to the first ignition by the first ignition plug 51, the second ignition by the second ignition plug 52 is executed. Also good. In this case, since the ignitability of the pre-spray can be improved even in a high load region, the stability of diesel combustion can be improved.

  Further, when the internal combustion engine 1 includes a so-called EGR device that introduces a part of the exhaust gas into the intake system as EGR gas, the EGR gas is an inert gas. The ignitability decreases. Therefore, in this case, when the EGR rate of the intake air is higher than a predetermined value, the second ignition by the second ignition plug 52 is performed in addition to the first ignition by the first ignition plug 51, similarly to the low load combustion control described above. May be executed. According to this, it is possible to improve the ignitability of the pre-spray when the EGR rate of the intake air is high.

  Further, when the internal combustion engine 1 is provided with means for detecting the occurrence of misfire in the internal combustion engine 1 based on the engine speed or the pressure in the cylinder 2, etc., when the misfire is detected by the means, In addition to the first ignition by the first spark plug 51, the second ignition by the second spark plug 52 may be executed.

[Reference example]
The configuration of the internal combustion engine according to this reference example is the same as that of the above embodiment. In this reference example, as in the above embodiment, pre-combustion is performed by igniting the pre-spray formed by the first injected fuel with the spark plug, and the flame generated by the pre-combustion is used as a starting point. Main combustion is performed in which the unburned residue of the second injected fuel and the first injected fuel is self-ignited or diffusely burned. However, in this reference example, the ignition mode by the spark plug when performing the pre-combustion is different from that in the above embodiment.

FIG. 9 shows the engine load of the internal combustion engine 1, the ignition timing by the first spark plug 51 and the second spark plug 52, the first injected fuel amount, and the first injected fuel when performing pre-combustion according to this reference example. It is a figure which shows the correlation with the unburned residue rate. As shown in FIG. 9, in the present reference example, the first injected fuel amount increases as the engine load of the internal combustion engine 1 increases. In the low load region where the engine load is equal to or less than the predetermined load Qe1, ignition is performed by the first spark plug 51 and the second spark plug 52 during pre-combustion. Here, when the engine load of the internal combustion engine 1 is the minimum load Qemin in the low load region (for example, the engine load during idling), the ignition timing (that is, the first timing) by the first spark plug 51 in the basic combustion control of the above-described embodiment. The first ignition plug 51 and the first ignition plug 51 are set at the same timing as the first ignition interval at which the spray injection combustion is possible. Both ignitions with the two spark plugs 52 are performed simultaneously. As the first injection timing is advanced because the first injected fuel amount increases in accordance with the increase in engine load, the ignition timing (first ignition timing) by the first spark plug 51 and the second ignition plug The ignition timing (second ignition timing) by 52 is also advanced. However, at this time, the first ignition timing is advanced so as to be maintained at the basic ignition timing, while the second ignition interval is the first ignition timing, and the second ignition interval is the first ignition timing. The angle is advanced so as to increase as the amount of injected fuel increases. That is, the advance amount with respect to the increase amount of the first injected fuel amount is smaller at the second injection timing than at the first injection timing. Further, in the high load region where the engine load is higher than the predetermined load Qe1, ignition is performed only by the second spark plug 52 during pre-combustion. At this time, the second ignition timing is controlled to be the basic ignition timing.

  As shown in FIG. 3, in the internal combustion engine 1, not only the first spark plug 51 but also the second spark plug 52, the fuel spray injected from the injection hole 6 a of the fuel injection valve 6 has its ignitable region 52 a. It is installed at a position where it can pass, that is, at a position where spray guide combustion is possible even by ignition by the second spark plug 52. Therefore, ignition is performed by the second ignition plug 52 in addition to the first ignition plug 51 at the basic ignition timing, so that the first fuel injection amount burned by the spray guide combustion becomes the largest. Therefore, in the present reference example, as described above, when the engine load is the minimum load Qemin, that is, when the first injected fuel amount is the smallest, the first ignition plug 51 and the second ignition plug 52 are at the basic ignition timing. Ignition by both at the same time. Thereby, in this reference example, when the engine load is the minimum load Qemin, the unburned rate of the first injected fuel becomes the smallest.

  In the low load region, when the first injected fuel amount increases as the engine load increases, the second ignition timing is retarded with respect to the basic ignition timing while maintaining the first ignition timing at the basic ignition timing. The greater the retard amount of the second ignition timing with respect to the basic ignition timing (that is, the second ignition interval), the larger the ignition possible region of the second spark plug 52 when fuel is injected from the fuel injection valve 6 at the first injection timing. The second ignition is executed at a timing when the fuel spray that has passed through 52a deviates from the ignitable region 52a. Therefore, the first injected fuel that is burned by the ignition by the second spark plug 52 is reduced. Therefore, the unburned rate of the first injected fuel increases.

  In the high load region where the first injected fuel increases from the low load region, spray guide combustion is performed only by ignition by the second spark plug 52. In this case, the unburned ratio of the first injected fuel increases as compared with the case where both the first spark plug 51 and the second spark plug 52 are ignited. Therefore, the unburned rate of the first injected fuel is higher in the high load region than in the low load region. In the high load region, the first injected fuel amount increases compared to the low load region, so that the penetration of pre-spray is large. Therefore, the second spark plug 52 (L1 <L2 in FIG. 2) having a larger distance from the fuel injection position of the fuel injection valve 6 is a spark plug that ignites the pre-spray to perform spray guide combustion. More suitable than one spark plug 51. Therefore, in the high load region where spray guide combustion is performed with one spark plug, ignition by the second spark plug 52 is executed at the basic ignition timing.

  By controlling the first spark plug 51 and the second spark plug 52 as described above during pre-combustion, as shown in FIG. 9, the first injected fuel amount increases as the engine load increases. The unburned rate of the first injected fuel can be increased. Thereby, it is possible to suppress an increase in smoke accompanying an increase in the first injected fuel amount.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Piston 51 ... 1st spark plug 52 ... 2nd spark plug 6 ... Fuel injection valve 7 ... Intake port 8 ... Exhaust port 9 ... Intake valve 10 ・ ・ Exhaust valve 20 ・ ・ ECU
21 ·· Crank position sensor 22 · · Accelerator position sensor 71 · · Throttle valve 72 · · Air flow meter

Claims (1)

A control device for an internal combustion engine in which a swirl flow that is a swirl flow around a cylinder central axis is generated in a combustion chamber,
A fuel injection valve that has a plurality of injection holes and injects fuel from the vicinity of the cylinder central axis toward the cylinder wall surface in the combustion chamber;
A first ignition device whose relative position to the fuel injection valve is determined so that the spray injected from the fuel injection valve passes through the ignitable region and can be directly ignited;
The first injection by the fuel injection valve is executed at the first injection timing during the compression stroke, and the pre-spray formed by the first injection is ignited by the first ignition device, thereby injecting by the first injection. A pre-combustion unit that performs pre-combustion to burn a portion of the fuel that has been discharged
The fuel injected after the ignition to the pre-spray by the first ignition device and before the top dead center of the compression stroke, and the interval from the first injection timing starts from the flame generated by the pre-combustion By starting execution of the second injection by the fuel injection valve at a second injection timing that becomes a predetermined injection interval set to start combustion of the fuel, fuel self-ignition is generated and at least the second In a control device for an internal combustion engine, comprising: a main combustion unit that performs main combustion for diffusing and burning a part of fuel injected by injection,
The distance from the fuel injection position of the fuel injection valve in the combustion chamber is within a predetermined region defined by an angle of less than 180 degrees in the swirl flow rotation direction starting from the first ignition device. A second ignition device installed at a position larger than the device;
When the pre-combustion unit performs the pre-combustion, the pre-combustion section is set to a predetermined second ignition timing that is after the first ignition timing that is the ignition timing in the first ignition device and before the second injection timing. A control device for an internal combustion engine that performs ignition by the second ignition device.

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