JP2002276442A - Combustion control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely control the self-ignition timing, securing a nitrogen oxide reducing effect by compression self-ignition combustion. SOLUTION: The device is provided with a direct injection type fuel injection device 8 and an ignition plug 9. By performing a first fuel injection for a period till the first half of a compression stroke, and sparking and igniting air-fuel mixture formed by the fuel injection, combustion of a first stage is performed. Subsequently, a second fuel injection is performed to burn the injection fuel. By making residual fuel perform self-ignition due to a rise in temperature within a combustion chamber by the combustion, combustion of a second stage is performed. In this case, an injection timing for the second fuel injection is controlled according to the rise speed of the combustion pressure in the combustion of the first stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-cycle type direct injection spark ignition compression self-ignition internal combustion engine such as a gasoline engine for automobiles, for example, a plurality of fuel injections and ignition for compression self-ignition combustion. Accordingly, the present invention relates to a combustion control device for an internal combustion engine that obtains a desired combustion timing.

[0002]

2. Description of the Related Art Compression self-ignition combustion starts at a plurality of points in a combustion chamber, and is therefore leaner than normal spark ignition combustion (combustion in which a flame generated by a spark propagates throughout the combustion chamber). Because stable combustion can be obtained even at a low air-fuel ratio,
It is possible to improve fuel efficiency. In addition, there is also an advantage that the combustion temperature is lowered because the air-fuel mixture having a very lean air-fuel ratio is burned, and the generation amount of NOx can be greatly reduced.

However, in the conventional compression self-ignition combustion, the combustion start timing (self-ignition timing) is dominated by the pre-reaction speed of the fuel which progresses according to the change in temperature and pressure due to the compression of the piston. If the temperature / pressure history during the compression stroke changes due to a change in (temperature or pressure of the intake air), a change in the cylinder wall temperature, an EGR amount, or the like, a sudden increase in in-cylinder pressure due to premature ignition or a delay in ignition timing There is a problem that unstable combustion occurs.

[0004] Techniques for solving such problems include:
There is one disclosed in JP-A-10-196424. In this technology, it is ensured that self-ignition does not occur until the top dead center of compression only by the compression action of the piston,
An additional temperature rise is applied near the compression top dead center to generate auto-ignition. According to this conventional technique, even if the temperature / pressure history during the compression stroke slightly changes, self-ignition can be generated at any time.

[0005] As a method for making the above technique concretely practicable, there is a method disclosed in Japanese Patent Application Laid-Open No. H11-210539, in which an existing spark plug is used to provide an additional temperature rise. I have. That is, according to this technique, one of the EGR amount, the opening timing of the intake valve, the compression ratio, the supercharging pressure, and the opening timing of the exhaust valve is adjusted so that the in-cylinder temperature at the end of the compression stroke falls within the target temperature range. Under the control, when the in-cylinder temperature falls within the target temperature range, spark ignition is executed to additionally increase the in-cylinder temperature, whereby the remaining fuel is self-ignited.

[0006]

However, if the air-fuel ratio in the cylinder is made significantly lean, the range in which the flame generated by spark ignition propagates becomes very narrow, and the temperature rise that can be additionally provided is increased. Becomes smaller. In this case, the allowable range for the change in the temperature / pressure history during the compression stroke becomes small, and it becomes difficult to control the ignition timing. On the other hand, when the degree of lean is reduced, the range of flame propagation combustion can be expanded, but the NOx reduction effect decreases.

[0007] Japanese Patent Application Laid-Open No. H11-210539 also describes that a mixture in a cylinder is stratified.
If a relatively rich air-fuel mixture layer can be formed near the spark plug while greatly reducing the air-fuel ratio in the entire cylinder, it is possible to secure an additional temperature rise width by spark ignition and to increase NOx.
It is considered that it is possible to achieve both the reduction effect and the reduction effect.

However, in order to realize such a stratified state, a complicated combustion chamber shape is required, which becomes a factor of deteriorating the output performance at the time of high load operation in which ordinary spark ignition combustion is performed. The present invention has been made in view of such a problem, and it is possible to reliably control the self-ignition timing while securing a NOx reduction effect by self-ignition combustion without adopting a complicated combustion chamber shape. The purpose is to do.

[0009]

According to a first aspect of the present invention, there is provided an air-fuel mixture comprising a fuel injection device for directly injecting fuel into a combustion chamber, and a spark plug. In a combustion control device for an internal combustion engine that burns by self-ignition, a first fuel injection is performed during a period up to the first half of a compression stroke, and a fuel-air mixture formed by the fuel injection is spark-ignited. Injection is performed to burn the injected fuel, and the remaining fuel is self-ignited by a rise in temperature and pressure in the combustion chamber due to the combustion.

According to the invention of claim 2, means for detecting a rising speed of a combustion pressure in the combustion caused by the spark ignition, and
Means for controlling the injection timing of the second fuel injection. According to a third aspect of the present invention, in particular, in the second aspect of the present invention, the means for controlling the injection timing of the second fuel injection is provided when the rising speed of the combustion pressure is faster than a set value. The injection timing of the second fuel injection is advanced when the rising speed of the combustion pressure is slower than a set value.

According to a fourth aspect of the present invention, means for determining the presence or absence of knocking and controlling the injection timing of the second fuel injection according to the presence or absence of knocking so as to delay at least when it is determined that knocking is present. Means. In the invention of claim 5, means for determining combustion stability, and means for controlling the injection timing of the second fuel injection so as to advance according to the combustion stability at least when it is determined that combustion is unstable. , Is provided.

According to a sixth aspect of the present invention, the injection amount of the second fuel injection increases as the rotation speed and the load increase. The invention of claim 7 is characterized in that the injection timing of the first fuel injection is retarded as the load decreases and the rotation speed increases. The invention of claim 8 is characterized in that the ignition timing of the spark ignition is retarded as the rotation speed and the load increase.

According to a ninth aspect of the present invention, the injection timing of the second fuel injection is set in advance so as to be retarded as the rotation speed and the load become higher.

[0014]

According to the first aspect of the present invention, combustion is performed in the following process. (1) When spark-ignition is performed on the air-fuel mixture formed by the first fuel injection, the fuel near the spark plug is partially oxidized by the energy of the ignition and reformed into active species such as aldehyde. When the energy of ignition is large, combustion proceeds through a partial oxidation reaction, and the gas temperature in the region near the ignition plug becomes high.

(2) At this time, when the second fuel injection is performed, the injected fuel starts burning before the surrounding air-fuel mixture. This is because the active species generated by spark ignition and the high-temperature gas generated by combustion after spark ignition become the ignition source, igniting part of the injected fuel, and this flame propagates throughout the spray area where the fuel density is high. It is thought to be. (3) The temperature and pressure in the combustion chamber increase due to this combustion, and the remaining fuel self-ignites and burns.

According to the above-described combustion process, a sufficient amount of fuel (fuel by the second fuel injection) necessary for controlling self-ignition combustion can be reliably burned.
Moreover, since the fuel injected by the second fuel injection surely burns without being concentrated near the spark plug,
There is no need to employ a complicated combustion chamber shape. In the present specification, combustion in which the air-fuel mixture formed by the first fuel injection burns (including a partial oxidation reaction) by spark ignition is referred to as first-stage combustion, and combustion (second fuel) generated thereafter is performed. The combustion of the injected fuel by injection and the self-ignition combustion of the remaining fuel) are referred to as second stage combustion.

According to the second aspect of the present invention, when a part of the air-fuel mixture is actively burned by spark ignition, the rising speed of the combustion pressure in this combustion is detected, and the second fuel By controlling the injection timing of the injection, the heat generation rate can be suitably controlled. In particular, when the rising speed of the combustion pressure is higher than a set value as in the invention of claim 3, by delaying the injection timing of the second fuel injection, it is possible to delay the subsequent self-ignition combustion and prevent knocking. Conversely, when the rising speed of the combustion pressure is lower than the set value, by advancing the injection timing of the second fuel injection, the subsequent self-ignition combustion can be accelerated, and misfire and combustion instability can be prevented. .

According to the fourth aspect of the present invention, when knocking is detected, knocking can be reliably prevented by controlling the injection timing of the second fuel injection to be retarded. According to the fifth aspect of the invention, when the combustion instability is detected, the injection timing of the second fuel injection is controlled to be advanced, so that the deterioration of the combustion stability can be reliably prevented.

According to the sixth aspect of the present invention, even when the ignition timing is delayed to prevent knocking during high rotation and high load,
By increasing the injection amount of the second fuel injection, subsequent self-ignition can be caused. As a result, the compression self-ignition combustion operation region can be extended to a high rotation and high load region. According to the invention of claim 7, as the load becomes lower and the engine speed becomes higher, the injection timing of the first fuel injection is retarded, and the fuel is concentrated around the ignition plug, so that the mixture concentration becomes lower at the time of a lower load. It becomes possible to prevent the ignition from becoming excessive and becoming impossible.

According to the eighth aspect of the invention, the ignition timing is retarded as the rotation speed and the load become higher, so that the combustion due to the spark ignition can be prevented from sharpening and the occurrence of knocking can be prevented. According to the ninth aspect of the invention, the injection timing of the second fuel injection is preset so as to be retarded as the rotation speed and the load become higher, so that the subsequent self-ignition becomes rapid combustion and knocking occurs. Can be prevented from occurring.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a four-cycle automobile gasoline engine which is a direct injection spark ignition compression self-ignition internal combustion engine will be described below with reference to the drawings. FIG. 1 is a system diagram showing an embodiment of a direct injection spark ignition compression self-ignition internal combustion engine according to the present invention.

In a combustion chamber 4 defined by the cylinder 1, the cylinder head 2 and the piston 3, air controlled by a throttle valve (not shown) is supplied from an intake manifold 5 and an intake port 6 constituting an intake passage. It is sucked when the valve 7 is opened. A fuel injection device (fuel injection valve) 8 is attached to the cylinder head 2 so as to be positioned on the intake side of the combustion chamber 4 and injects fuel directly into the combustion chamber 4. A spark plug 9 for spark ignition is mounted in a position.

The exhaust gas after combustion is exhausted from an exhaust port 11 and an exhaust manifold 12 constituting an exhaust passage when the exhaust valve 10 is opened. An EGR passage 13 is provided for returning a part of the exhaust gas from the exhaust manifold 12 to the intake manifold 5, and the EGR passage 13 has an EGR amount (E
An EGR control valve 14 capable of adjusting the GR rate is interposed.

An electronic control unit (engine control unit; hereinafter referred to as an ECU) 20 for controlling the engine has a microcomputer built therein, which includes a crank angle signal from a crank angle sensor 31 (the engine rotation speed N). Is detected), an accelerator opening signal from the accelerator opening sensor 32 (the engine load T can be detected thereby) is input, and if necessary, an intake air amount signal from an air flow meter (not shown), an intake air temperature Intake temperature signal from sensor (not shown), exhaust temperature sensor (not shown)
An exhaust temperature signal from the controller is also input.

Further, for detecting the in-cylinder pressure (combustion pressure) or knocking, for example, a piezoelectric in-cylinder pressure sensor 33 attached in a washer shape to the spark plug 9 is provided, and its signal is also input to the ECU 20. I have. The ECU 20
The operation of the fuel injection device 8, the spark plug 9, and the operation of the EGR control valve 14 are controlled based on these input signals.

In particular, in this internal combustion engine, in order to perform combustion control according to the operating conditions, the ECU 20 determines which of the combustion of the spark ignition combustion and the compression self-ignition combustion (spark ignition compression self-ignition combustion) according to the operating conditions. And a fuel injection amount control unit 22 and a fuel injection timing control unit 23 that control a combustion parameter to be optimal for each combustion mode according to the determination result. , Ignition timing control unit 24, E for controlling in-cylinder temperature
A GR rate control unit 25 is provided. However, these are realized as microcomputer programs.

Next, the combustion control in this embodiment will be described. Under the above configuration, in the present embodiment, it is possible to switch between spark ignition combustion and compression self-ignition combustion in accordance with the engine speed and the operating conditions of the load. As shown in FIG. Compression self-ignition combustion is performed in a specific operation region (low-medium rotation / low-medium load region) based on N and load T, and spark ignition combustion is performed in other operation regions.

In the compression self-ignition combustion, the first fuel injection is performed in a period up to the first half of the compression stroke, and the first-stage combustion is performed by spark-igniting the air-fuel mixture formed by the fuel injection. The second fuel injection is performed to burn the injected fuel (second stage combustion), and the remaining fuel is caused to self-ignite combustion (second stage combustion) by the rise in temperature and pressure in the combustion chamber due to this combustion.

FIG. 3 shows an example of the change of the in-cylinder pressure with respect to the crank angle at the time of the compression self-ignition combustion. 1 in the figure
The second cylinder pressure peak corresponds to the first stage combustion, and the second cylinder pressure peak corresponds to the second stage combustion. In compression self-ignition combustion, as shown in FIG. 4, there is a correlation between the pressure rise rate and the knocking strength, and it is clear that the knocking strength increases as the pressure rise rate increases. The pressure rise rate dP / dtmax in the figure is the maximum pressure rise rate in one cycle.

Further, as shown in FIG. 5, with the increase in the combustion period, the piston is lowered during the combustion period, so that the combustion becomes incomplete and the combustion efficiency (the actual combustion with respect to the calorific value of the injected fuel). It is clear that the ratio of the calorific value of the fuel decreases. The combustion period θ10−
90 is a period from the crank angle at which 10% of the fuel injected into the combustion chamber is burned to the crank angle at which 90% of the fuel is burned, and is one parameter representing the combustion period.

Therefore, when the combustion is completed within a certain crank angle so as not to lower the combustion efficiency, the real time during which the combustion is performed is reduced and the rate of pressure rise per unit time is increased. As the load increases and the rate of pressure rise per unit time increases, the higher the load, the more likely knocking occurs, making it difficult to expand the compression self-ignition operation region.

FIG. 6 shows the relationship between the pressure increase rate dP / dtmax with respect to the engine speed N, the load T, and the combustion timing θ50. θ50 is 50% of the fuel injected into the combustion chamber
Is the crank angle at which combustion has taken place, and is one parameter representing the combustion timing. As can be seen from this figure, with the same rotational speed or the same load, the more the combustion timing is retarded from the top dead center, the lower the pressure rise rate. This is because the combustion is performed when the piston descends, and the pressure rise rate during combustion is suppressed by the decrease in pressure due to the piston descending.

Therefore, 50 of the fuel injected into the combustion chamber
The combustion timing θ50 represented by the crank angle at which% is burned is assumed to be after the top dead center, and as shown in FIG. 7, knocking is prevented by controlling so as to further delay the engine speed N or the load T as the engine speed N increases. As a result, the compression auto-ignition combustion operation range can be expanded. Therefore, the first fuel injection timing, the second fuel injection timing, and the first-stage combustion are set so that an appropriate combustion timing (start timing of the second-stage combustion) is obtained according to the operating conditions of the engine. Ignition timing to start, first
Control of the injection amount ratio of the second fuel injection to the second fuel injection (the second injection amount ratio with respect to the total injection amount), the EGR rate, and the like. In particular, in the present invention, combustion is performed in the following combustion process. Let

FIG. 8 shows a combustion process according to the present invention. In the present invention, the first-stage combustion is performed by performing spark ignition on the air-fuel mixture formed by the first fuel injection, and then the second-stage combustion is performed by performing the second fuel injection. Control. At the time point a in the figure, the first fuel injection is performed by the fuel injection device 8. As a result, the fuel and the air are sufficiently mixed, and a substantially homogeneous air-fuel mixture is formed in the entire region in the cylinder.

At the time point b in the figure, spark ignition is performed on the air-fuel mixture by the spark plug 9. Thereby, the fuel near the ignition plug 9 burns (first stage combustion). The area where the flame has propagated becomes hot, and the surrounding temperature and pressure also increase. At the time point c in the figure, the fuel injection device 8
Fuel injection. Thereby, the fuel in the spray region burns. This combustion occurs because the fuel density is high in the spray area, so that when the spray area reaches the high temperature area formed by spark ignition, it partially ignites, and this flame propagates throughout the spray area. It is thought that it is. In this case, it is sufficient that the spray passes near the spark plug 9, and it is not necessary to concentrate the fuel near the spark plug 9. This combustion further increases the surrounding temperature and pressure, and the remaining fuel self-ignites and burns (second stage combustion).

As described above, the second-stage combustion includes the flame-propagation combustion of the fuel spray by the second fuel injection and the self-ignition combustion of the remaining fuel in the air-fuel mixture formed by the first fuel injection. Made by The flow of combustion control according to the present invention performed based on the above will be described with reference to a flowchart.

First, the combustion control according to the first embodiment of the present invention will be described with reference to the flowchart of FIG. In S1, the engine speed N and the load T are detected. In S2, based on the engine speed N and the load T, based on the map of FIG.
The combustion mode is determined to be in the spark ignition combustion operation region or the compression self-ignition combustion operation region. If it is determined that spark ignition combustion is to be performed, the process proceeds to S3, and normal spark ignition combustion control is performed.

On the other hand, when it is determined that the compression self-ignition combustion is to be performed, the control of the compression self-ignition combustion shown in S4 to S16 is performed. Hereinafter, control of the compression self-ignition combustion will be described. In S4, based on the map of FIG. 11, an EGR rate for appropriately raising the cylinder temperature with the EGR gas is calculated from the engine speed N and the load T. Where E
The GR rate is set to be larger as the rotation becomes higher and the load becomes lower. That is, the EGR rate is increased with an increase in the rotation speed, thereby preventing a decrease in the stability of the compression self-ignition combustion when the combustion timing is retarded. Also, the stability of compression self-ignition combustion is prevented from lowering by increasing the EGR rate at a lower load, and knocking is prevented by decreasing the EGR rate with an increase in the load.

In S5, EG is determined based on the map shown in FIG.
The EGR control valve opening is calculated and controlled from the R rate and the actually detected exhaust gas temperature. Here, the opening degree of the EGR control valve is set to be larger as the EGR rate increases and to be set larger as the exhaust gas temperature decreases. As the target EGR rate increases, it is natural that the EGR control valve opening is increased. However, the in-cylinder temperature is indirectly detected based on the exhaust gas temperature. The opening of the EGR control valve is corrected to a large side, and conversely, as the exhaust gas temperature increases, the opening of the EGR control valve is corrected to a small side. Therefore, the intake air temperature may be used instead of the exhaust gas temperature. However, when the combustion timing control based on the EGR rate is not performed, S4 and S5 are omitted.

At S6, the first fuel injection amount q1 and the second
Is calculated. For details, first, FIG.
The second injection amount ratio M to the total injection amount q is calculated from the engine rotation speed N and the load T based on the map shown in FIG. Here, the second injection amount ratio M is set to increase as the rotation speed and the load increase. Then, the first fuel injection amount q1
= Total injection amount q x (1-M), second fuel injection amount q2 = total injection amount q x M. The total injection amount q is calculated from the intake air amount, the engine speed, the target air-fuel ratio, and the like by a known method.

The reason why the second fuel injection amount q2 is increased as the rotation speed and the load become higher is that the ignition timing IGT becomes higher and the rotation speed becomes higher.
In order to increase the heat generation by increasing the ratio of the second injection amount to the total injection amount in order to ensure that the subsequent compression self-ignition combustion is performed. It is. In S7, a first fuel injection timing IT1 and a second fuel injection timing TT2 are calculated.

The first fuel injection timing IT1 is calculated from the engine speed N and the load T based on the map shown in FIG. Here, the first fuel injection timing IT1 is set to the retard side as the engine speed increases and the load decreases. That is, by delaying the first fuel injection timing IT1 with an increase in the rotation speed, the leaning due to the dispersion of the air-fuel mixture is suppressed, and the deterioration of the combustion stability is prevented. Also, the first fuel injection timing I
By advancing T1 with an increase in load, fuel is dispersed in the combustion chamber, enrichment of the air-fuel mixture due to an increase in fuel injection amount is suppressed, and a sudden increase in pressure is prevented. By concentrating the fuel around the spark plug, it is possible to prevent the concentration of the air-fuel mixture from becoming too low at a low load, thereby preventing ignition from becoming impossible.

The second fuel injection timing IT2 is calculated from the engine speed N and the load T based on the map shown in FIG. Here, the second fuel injection timing IT2 is set to the retard side as the rotation speed and the load become higher. That is, by delaying the second fuel injection timing IT2 in accordance with the retardation of the ignition timing IGT due to the increase in the rotation speed and the load, the subsequent self-ignition becomes a rapid combustion and the occurrence of knocking is prevented. . However, the second fuel injection timing IT2 set here is a basic set value and will be corrected later.

In S8, an ignition timing IGT is calculated from the engine speed N and the load T based on the map shown in FIG. Here, the ignition timing IGT is set to the retard side as the rotation speed and the load become higher. That is, the ignition timing IG
By delaying T with an increase in the rotation speed and the load, the combustion subsequent to the spark ignition combustion is prevented from becoming abrupt combustion.

At S9, the first fuel injection is executed. That is, at the first fuel injection timing IT1 set in S7, the fuel injection of the first fuel injection amount q1 set in S6 is performed. In S10, ignition is performed. That is,
At the ignition timing IGT set in S8, ignition is performed.

In step S11, a change in the in-cylinder pressure (combustion pressure) P after ignition is detected by the in-cylinder pressure sensor.
The pressure rise rate dP / dt is calculated. In S12, the detected pressure increase rate dP / dt is compared with a set value. As a result of the comparison, when the pressure rise rate dP / dt is smaller than the set value, the process proceeds to S13, in order to prevent the deterioration of combustion stability,
In order to advance the second injection timing IT2 (here, an advance value from a predetermined crank angle position), the injection timing correction amount ΔIT2 is increased (ΔIT2 = IT2 + C; C is a predetermined increment).

On the other hand, if the pressure increase rate dP / dt is larger than the set value, the process proceeds to S14, in which the injection timing correction amount ΔIT2 is decreased to retard the second injection timing IT2 in order to prevent knocking. (ΔIT2 = IT2-
C). In S15, the second fuel injection timing IT2 is corrected based on the injection timing correction amount ΔIT2 increased or decreased in S13 or S14 (IT2 = IT2 + ΔIT2).

At S16, the second fuel injection is executed.
That is, at the second fuel injection timing IT2 set in S7 and corrected in S15, the fuel injection of the second fuel injection amount q2 set in S6 is performed. By controlling in this manner, combustion can be performed at an optimal time according to the engine speed and the load, and the combustion pressure rise rate (dP / d) in the first-stage combustion by spark ignition
t) is feedback-controlled near the set value, so that deterioration of combustion stability and occurrence of knocking can be prevented. Here, in particular, the portion of S11 corresponds to a means for detecting the rising speed of the combustion pressure in the first stage combustion by spark ignition.
Steps S12 to S15 correspond to means for controlling the injection timing of the second fuel injection according to the rising speed of the combustion pressure.

Next, the combustion control according to the second embodiment of the present invention will be described with reference to the flowchart of FIG. Second
Except for the part related to the correction of the fuel injection timing IT2,
This is the same as the embodiment (FIG. 9), and S11 to S15 in FIG.
, S20 and S21 to S24 are provided, and only different portions will be described.

At S7, the first and second fuel injection timings IT
After setting 1, IT2, the second fuel injection timing IT2 is corrected in S20. That is, based on the injection timing correction amount ΔIT2 increased or decreased in S21 to S24 described later in the previous cycle, the second fuel injection timing IT
2 (IT2 = IT2 + ΔIT2). After performing the first fuel injection in S9, the ignition in S10, and the second fuel injection in S16, the process proceeds to S21.

In step S21, the presence or absence of knocking is determined based on the signal from the in-cylinder pressure sensor used as a knocking sensor. When knocking is detected, the process proceeds to S22,
In order to retard the second fuel injection timing IT2, the injection timing correction amount ΔIT2 is decreased (ΔIT2 = IT2-
C). Thus, in the next cycle, the second fuel injection timing IT2 can be corrected to the retard side, and knocking can be prevented.

If there is no knocking, the process proceeds to S23.
In S23, the rotation fluctuation is detected from the signal of the crank angle sensor, and the combustion stability is determined based on the detected rotation fluctuation. When the combustion instability is detected, the process proceeds to S24, and the injection timing correction amount ΔIT2 is increased to advance the second fuel injection timing IT2 (ΔIT2 = IT2 + C). This makes it possible to correct the second fuel injection timing IT2 to the advanced side in the next cycle, thereby preventing combustion instability.

By performing such control, combustion can be performed at an optimum time according to the engine speed and load.
Further, occurrence of knocking and deterioration of combustion stability can be prevented. Here, in particular, the portion of S21 corresponds to knocking determination means, and the second portion of the case where knocking is present in the portion of S22.
Of the fuel injection timing. The step S23 corresponds to a means for determining combustion stability, and the step S24 corresponds to a means for controlling the second fuel injection timing when combustion is unstable.

In the two embodiments described above, a part of the air-fuel mixture is completely burned by spark ignition, and the fuel of the second fuel injection is burned by this combustion. Combustion may be a partial oxidation reaction only for reforming the fuel into active species. Any type of fuel injection valve may be used as long as it can inject fuel directly into the combustion chamber, but the use of a high-pressure air-assisted injection valve that injects a mixture of high-pressure air and fuel is particularly effective. is there. That is, it is desirable that the fuel of the first fuel injection be sufficiently mixed with the air at the time of performing the spark ignition (the spark ignition is performed on an air-fuel mixture that is insufficiently mixed and has a local air-fuel ratio unevenness). Then, the amount of heat generated by the first-stage combustion becomes unstable, or the fuel is burned by spark ignition performed only for fuel reforming.) When using a normal fuel injection valve, The first fuel injection timing cannot be set too late. In contrast, a high-pressure air-assisted injection valve that injects fuel mixed with air in advance can achieve desired first-stage combustion even if spark ignition is performed immediately after injection. It is also possible to set the timing to the compression stroke.

[Brief description of the drawings]

FIG. 1 is a system diagram of an internal combustion engine showing an embodiment of the present invention.

FIG. 2 is a diagram showing an operation region in which compression self-ignition combustion is performed.

FIG. 3 is a diagram showing a change in in-cylinder pressure during compression self-ignition combustion.

FIG. 4 is a diagram showing a relationship between a pressure rise rate and knocking strength.

FIG. 5 is a diagram showing a relationship between a combustion period and combustion efficiency.

FIG. 6 is a diagram showing a relationship between a rotational speed, a load, a combustion timing, and a pressure rise rate.

FIG. 7 is a diagram showing a preferable combustion timing with respect to a rotation speed and a load.

FIG. 8 is a diagram showing a combustion process in the present invention.

FIG. 9 is a flowchart of combustion control according to the first embodiment.

FIG. 10 is a flowchart of combustion control according to a second embodiment.

FIG. 11 is a characteristic diagram of an EGR rate with respect to a rotation speed and a load.

FIG. 12 is a characteristic diagram of an EGR control valve opening degree with respect to an EGR rate and an exhaust gas temperature.

FIG. 13 is a characteristic diagram of a second injection amount ratio with respect to a rotation speed and a load.

FIG. 14 is a characteristic diagram of a first fuel injection timing with respect to a rotation speed and a load.

FIG. 15 is a characteristic diagram of a second fuel injection timing with respect to a rotation speed and a load.

FIG. 16 is a characteristic diagram of ignition timing with respect to rotation speed and load.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Cylinder head 3 Piston 4 Combustion chamber 5 Intake manifold 6 Intake port 7 Intake valve 8 Fuel injection device 9 Spark plug 10 Exhaust valve 11 Exhaust port 12 Exhaust manifold 13 EGR passage 14 EGR control valve 20 ECU 21 Combustion type determination unit 22 Fuel injection amount control unit 23 Fuel injection timing control unit 24 Ignition timing control unit 25 EGR rate control unit 31 Crank angle sensor 32 Accelerator opening sensor 33 In-cylinder pressure sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 43/00 301 F02D 43/00 301B 301J 45/00 368 45/00 368S 368B F02P 5/152 F02P 5 / 15D 5/153 17/00 R 17/12 (72) Inventor Masatsugu Imazu 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside Nissan Motor Co., Ltd. (72) Inventor Akihiro Iiyama 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan F-term (reference) within Automobile Co., Ltd. FA38 3G301 HA02 HA04 HA13 HA15 HA18 JA00 KA06 KA23 LA00 MA11 MA18 MA23 MA27 NC04 NE01 NE06 NE11 NE12 NE13 NE15 PA01Z PA10Z PA11Z PC01Z PC08Z PD11Z PE03Z

Claims (9)

[Claims] 1. A combustion control device for an internal combustion engine, comprising: a fuel injection device for directly injecting fuel into a combustion chamber; and a spark plug, wherein an air-fuel mixture formed in the combustion chamber is combusted by self-ignition. Performing a first fuel injection during the period, performing spark ignition on the air-fuel mixture formed by the fuel injection, and then performing a second fuel injection to burn the injected fuel;
A combustion control device for an internal combustion engine, wherein the remaining fuel is self-ignited by a rise in temperature and pressure in a combustion chamber due to the combustion. 2. A fuel cell system comprising: means for detecting a rising speed of a combustion pressure in combustion caused by the spark ignition; and means for controlling an injection timing of the second fuel injection in accordance with the rising speed of the combustion pressure. The combustion control device for an internal combustion engine according to claim 1, wherein: 3. The means for controlling the injection timing of the second fuel injection, wherein when the rising speed of the combustion pressure is faster than a set value, the injection timing of the second fuel injection is retarded. If the pressure rise speed is slower than the set value,
3. The combustion control device for an internal combustion engine according to claim 2, wherein the injection timing of the second fuel injection is advanced. 4. A means for judging the presence or absence of knocking, and means for controlling the injection timing of the second fuel injection so as to delay at least when it is judged that knocking is present, in accordance with the presence or absence of knocking. The combustion control device for an internal combustion engine according to claim 1, wherein: 5. A means for judging combustion stability, and means for controlling the injection timing of the second fuel injection so as to advance at least when it is judged that combustion is unstable in accordance with the combustion stability. The combustion control device for an internal combustion engine according to claim 1, wherein the combustion control device is provided. 6. The injection amount of the second fuel injection is high rotation,
The combustion control device for an internal combustion engine according to any one of claims 1 to 5, wherein the amount increases as the load increases. 7. The internal combustion engine according to claim 1, wherein the injection timing of the first fuel injection is retarded as the load decreases and the engine speed increases. Combustion control device. 8. The spark timing of the spark ignition is retarded as the rotation speed and the load become higher.
A combustion control device for an internal combustion engine according to claim 7. 9. The fuel injection system according to claim 1, wherein the injection timing of the second fuel injection is set in advance so as to be retarded as the rotation speed and the load increase.
A combustion control device for an internal combustion engine according to any one of the first to third aspects.