JP2002213278A - Combustion controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the ignition stability of self-igniting combustion of a compressive self-ignition type internal combustion engine without increasing the quantity of NOx discharged. SOLUTION: In a self-ignition combustion range, total injection period, number of injections, and the time to start injection are set according to engine load and engine speed which indicate ignitability. Multiple injections by which fuel is periodically injected twice or more during one cycle are carried out in accordance with the total injection period, number of injections and the time to start injection to create an air-fuel mixture with irregular variations in air-fuel ratio. The air-fuel mixture with the irregular variations in air-fuel ratio is easier to ignite than if a uniform air-fuel mixture is caused to self-ignite, because combustion is started from the rich portion of the mixture. Also, the air-fuel mixture can make smaller the quantity of NOx discharged than if it is stratified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control device for an internal combustion engine, and more particularly, to a technique for forming an air-fuel mixture in a compression self-ignition combustion operation.

[0002]

2. Description of the Related Art Conventionally, an engine for performing compression self-ignition combustion has been known. In the above-mentioned compression self-ignition combustion, since combustion is started simultaneously at multiple points in the combustion chamber, the combustion speed is high, and stable combustion can be realized even in a state where the air-fuel ratio is lean as compared with normal spark ignition combustion. The fuel consumption rate can be improved, and the combustion temperature can be reduced by burning the lean air-fuel mixture, the NOx in the exhaust gas can be significantly reduced, and the fuel and air can be sufficiently premixed. If so, the air-fuel ratio becomes more uniform and NOx can be further reduced.

[0003] Further, in the high rotation speed and high load range, normal spark ignition combustion is performed, and in the low rotation speed and low middle load range, the combustion mode is switched from spark ignition combustion to compression self-ignition combustion, thereby achieving high rotation speed and high load. It is possible to improve the fuel consumption rate and reduce NOx at low rotation speed and low medium load while ensuring high output sometimes. In a two-cycle spark ignition type internal combustion engine, self-ignition combustion in a combustion chamber is performed in order to avoid unstable combustion at a partial load and to reduce HC (unburned hydrocarbon) emissions. Technologies that have been actively used have been proposed.

For example, Japanese Patent Application Laid-Open No. 7-07279 discloses that the pressure and temperature in the cylinder at the start of the compression stroke are increased by increasing the residual gas concentration in the cylinder by blocking a part of the exhaust passage at a low load. A technique for controlling the combustion timing of self-ignition has been disclosed.

[0005]

When compression self-ignition combustion is performed using a low self-ignition fuel such as gasoline, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-071279, residual gas is not used. It is effective to make effective use of the heat energy possessed. Therefore, as a method for realizing compression self-ignition combustion in a four-cycle engine, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent No. 266878, at the time of transition from the exhaust stroke to the intake stroke, a closed period in which both the exhaust valve and the intake valve are closed is provided, so that residual gas is actively generated, and when the compression stroke is started. There was a method of increasing the cylinder internal pressure and temperature.

However, when the residual gas amount is increased, the filling efficiency is reduced, so that the compression auto-ignition combustion cannot be performed in the high load region, and the compression auto-ignition combustion can be performed in a narrow region on the low load side. However, there is a problem that the effect of improving fuel efficiency and emission is reduced. Japanese Patent Application Laid-Open No. H10-196424 discloses that when a pre-mixed air-fuel mixture is compressed, additional fuel (ignition oil) is injected near top dead center to increase the temperature due to the combustion of the ignition oil. U.S. Pat. No. 6,064,056 discloses a configuration for causing a premixed gas to self-ignite combustion.

[0007] In the case of the configuration in which the additional injection is performed as described above, the ignitability deteriorates when the air-fuel ratio of the premixed air becomes lean. Therefore, there is a problem that NOx is generated by the combustion of the ignition oil. Conventionally,
In spark ignition combustion, a method of improving the ignitability by stratifying an air-fuel mixture that locally generates a rich air-fuel mixture has been considered. However, when stratification is performed, NOx is emitted from a rich region. There is a problem that a large amount is generated and emission is deteriorated.

Japanese Patent Application Laid-Open No. H10-252570 discloses a technique for eliminating fuel lumps by providing a fuel portion and an air portion regularly in an air-fuel mixture to reduce emissions. However, there is a problem that the air-fuel mixture of the same concentration ignites at once and causes knocking due to the regular distribution of concentration. SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and a compression self-ignition type internal combustion engine has an N
An object of the present invention is to ensure ignition stability of self-ignition combustion without increasing the amount of Ox emission.

It is another object of the present invention to expand the operating region in which the compression self-ignition combustion operation can be performed and to improve the fuel efficiency and exhaust of the compression self-ignition internal combustion engine.

[0010]

Therefore, in the invention of claim 1, the air-fuel mixture in the combustion chamber has an irregular air-fuel ratio variation during the compression self-ignition combustion operation.
According to this configuration, the air-fuel mixture in the combustion chamber does not have a uniform air-fuel ratio and is not regularly divided into a rich region and a lean region as in the case of stratification. The mixture is formed so that the fuel ratio varies, and the self-ignition combustion starts from a rich portion in the formed mixture.

According to the second aspect of the present invention, during the compression self-ignition combustion operation, an additional temperature rise is applied to the main air-fuel mixture field to cause compression self-ignition combustion, and the main air-fuel mixture combustion is performed. In this configuration, irregular air-fuel ratio variations are provided. According to this configuration, the main mixture field is a mixture field that does not lead to self-ignition as it is, but only reaches compression self-ignition combustion due to an additional temperature rise. When a fuel ratio variation is provided and an additional temperature rise is applied, self-ignition combustion will start from the rich portion.

According to the third aspect of the present invention, after the fuel injection for forming the main mixture field, an additional fuel injection for forming a local rich mixture field is performed, and the local rich mixture is performed. The main mixture field is configured to be brought into compression self-ignition combustion by a temperature rise due to spark ignition combustion or compression self-ignition combustion of the air field. According to such a configuration, stratification of the air-fuel mixture forming a local rich air-fuel mixture field is performed by additional fuel injection after the formation of the main air-fuel mixture field, and the rich air-fuel mixture is spark-ignited and burned by a spark plug. Alternatively, by performing compression self-ignition combustion, the surrounding main air-fuel mixture field is converted from its rich portion to compression self-ignition combustion.

[0013] The invention according to claim 4 is configured such that the higher the rotational speed of the engine, the larger the air-fuel ratio variation. According to such a configuration, the air-fuel ratio variation is not constant, and the higher the rotation speed at which the ignitability of self-ignition combustion deteriorates,
Increase the variation (difference between the maximum air-fuel ratio and the minimum air-fuel ratio).

According to the fifth aspect of the present invention, the air-fuel ratio variation increases as the engine load decreases. According to such a configuration, the air-fuel ratio variation is not constant, and the variation (difference between the maximum air-fuel ratio and the minimum air-fuel ratio) increases as the load decreases at which the ignitability of the self-ignition combustion deteriorates.

According to the present invention, the combustion stability and knocking intensity of the engine are detected, and the air-fuel ratio variation is controlled so that the combustion stability and knocking intensity of the engine are respectively within allowable ranges. did. According to such a configuration, the combustion stability (torque fluctuation) of the engine is within an allowable range, and the knocking strength is within an allowable range.
The variation in the air-fuel ratio is feedback-controlled.

According to a seventh aspect of the present invention, the air-fuel mixture having an irregular air-fuel ratio is formed by multiple injections in which fuel is divided into two or more times during one cycle and periodically injected. . According to such a configuration, the fuel to be injected is not injected at once, but is divided into two or more times and injected little by little periodically, thereby causing irregular air-fuel ratio variations.

According to the present invention, the air-fuel ratio variation is controlled by the number of injections of the multiple injection. According to such a configuration, the variation in the air-fuel ratio increases as the number of injections of the multiple injections increases, so that the number of injections is changed according to the operating conditions (rotation, load, combustion stability, knocking intensity).

According to a ninth aspect of the present invention, the air-fuel ratio variation is controlled by a period during which the multiple injection is performed. According to such a configuration, as the period from the first injection to the final injection of the multiple injections becomes longer, the variation in the air-fuel ratio becomes larger, and therefore, depending on the operating conditions (rotation, load, combustion stability, knocking intensity). Change the injection period.

According to the tenth aspect of the present invention, the air-fuel ratio variation is controlled by the injection timing of the multiple injection. According to such a configuration, as the timing of performing the multiple injections is retarded, the variation in the air-fuel ratio increases,
Operating conditions (rotation, load, combustion stability, knocking strength)
Injection timing (injection start timing) is changed according to.

[0020]

According to the first aspect of the present invention, since the self-ignition combustion starts from the rich portion of the air-fuel mixture having irregular air-fuel ratio variations, when the air-fuel mixture having a uniform air-fuel ratio is formed. In comparison, the self-ignitability of the air-fuel mixture is improved, and the air-fuel ratio variation is smaller than in the case of forming a stratified air-fuel mixture.Therefore, NOx and soot generated by combustion in the rich portion are small, and the emission is not deteriorated. There is an effect that the stability of compression self-ignition combustion can be improved.

According to the second and third aspects of the present invention, it is possible to control the timing of the compression self-ignition combustion and to perform the highly stable compression self-ignition combustion without deterioration of the emission. According to the fourth and fifth aspects of the invention, there is an effect that the stability of the compression auto-ignition combustion can be maintained with respect to a change in load and rotation while suppressing deterioration of the emission.

According to the sixth aspect of the present invention, even if there is a change in the operating conditions or a variation in the engine, there is an effect that the compression self-ignition combustion can be performed with the knocking strength and the combustion stability within the allowable ranges. . According to the seventh aspect of the present invention, since irregular air-fuel ratio variations are provided by multiple injections in which fuel is divided into two or more times and injected periodically during one cycle, the hardware configuration of the fuel injection device is changed. In addition, there is an effect that the stability of compression self-ignition combustion can be improved.

According to the present invention, a desired air-fuel ratio variation can be provided by controlling the number of injections, the injection period, and the injection timing in the multiple injection, and the deterioration of the emission can be suppressed. In addition, there is an effect that the stability of the compression self-ignition combustion can be maintained with respect to a change in the operating condition.

[0024]

Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram showing a configuration of an embodiment in which a combustion control device for an internal combustion engine according to the present invention is applied to a gasoline engine. A gasoline engine 1 shown in FIG. 1 is a direct injection gasoline engine, and has a configuration in which compression self-ignition combustion and spark ignition combustion are switched according to operating conditions.

In the engine 1, an intake valve 4 is interposed in an intake port 3 communicating with the cylinder 2, and an exhaust valve 6 is arranged in an exhaust port 5 communicating with the cylinder 2.
Is interposed. The cylinder head 7 is formed in a pent roof type, the intake valve 4 and the exhaust valve 6 are arranged in a V shape, and a fuel injection valve 8 and a spark plug 9 are arranged in substantially the center of the pent roof type cylinder head 7. You.

An engine control unit (hereinafter referred to as ECU) 20 for controlling the injection amount and injection timing of the fuel injection valve 8 and the ignition timing of the ignition plug 9 includes:
A crank angle sensor signal from the crank angle sensor 10,
An accelerator opening signal from an accelerator opening sensor (not shown) is input. The ECU 20 determines which of the compression self-ignition combustion and the spark ignition combustion to operate in accordance with the operation conditions.
1. A spark ignition combustion control unit 22 for controlling the fuel injection valve 8 and the spark plug 9 during spark ignition combustion, and a self-ignition combustion control unit 23 for controlling the fuel injection valve 8 during compression self-ignition combustion.

As shown in FIG. 2, the combustion pattern judging section 21 judges the combustion mode based on the engine load T and the engine speed N. It is determined as a combustion region, and the other high load / high rotation regions are determined as spark ignition combustion regions. In addition, during compression self-ignition combustion, by performing multiple injections in which fuel is divided into two or more times and injected periodically during one cycle,
The air-fuel mixture in the combustion chamber has an irregular air-fuel ratio variation. The self-ignition combustion control unit 23 controls the number of injections control unit 24, the injection period control unit 25, and the injection timing control unit 26, The number of injections, the injection period, and the injection timing in the multiple injection are controlled.

FIG. 3 is a flowchart showing a first embodiment of the fuel injection control using the above hardware configuration. In step S11, the engine speed N and the engine load T are detected. In the present embodiment, the engine speed N is calculated based on the crank angle sensor signal, and the engine load T is represented by the accelerator opening.

In step S12, it is determined based on the detected engine speed N and engine load T whether the current operating condition is in the compression self-ignition combustion region or the spark ignition combustion region (see FIG. 2). . If it is determined in step S12 that the current is in the spark ignition combustion range, step S13
To supply the required amount of fuel in one injection during the intake stroke to form a premixed homogeneous mixture, and in the next step S14, the homogeneous mixture is sparked by the spark plug 9 Burn by ignition.

In the spark ignition combustion region, fuel may be injected in a plurality of injections. In addition, the fuel is injected not only during the intake stroke but also during the compression stroke to form a stratified mixture. Is also good. On the other hand, if it is determined in step S12 that it is in the compression self-ignition combustion region, the process proceeds to step S15,
A total injection period is set for multiple injections in which fuel is divided into two or more times and injected periodically during one cycle.

As shown in FIG. 4, the multiple injection is an injection in which injection is repeated a plurality of times with a pause period therebetween. The total injection period is defined as a period from the start of the first injection to the end of the last injection. Period. Although the injection time (injection pulse width) of each injection in the multiple injection is made uniform in FIG. 4, the injection time (injection pulse width) differs for each injection.
And the rest periods may be different for each.

In step S15, as shown in FIG. 5, a map in which the total injection period is stored in advance according to the engine speed N and the engine load T corresponds to the engine speed N and the engine load T at that time. Search and find the total injection period. Here, the total injection period is set longer as the engine rotation speed N is higher and the engine load T is smaller, as shown in FIG.
As the total injection period becomes longer, the air-fuel ratio (equivalent ratio) variation (difference between the maximum air-fuel ratio and the minimum air-fuel ratio) of the air-fuel mixture formed by the multiple injections increases.

In step S16, the number of injections indicating how many times the fuel is to be injected in the multiple injection is set. In the same manner as the total injection period, the number of injections is determined from the map (see FIG. 7) in which the number of injections is stored in advance according to the engine speed N and the engine load T, based on the engine speed N and the engine load T at that time. The corresponding number of injections is searched for and determined, and the number of injections is set higher as the engine speed N is higher and the engine load T is smaller.

When the number of injections is increased, as shown in FIG. 8, the air-fuel ratio (equivalent ratio) of the mixture formed by multiple injections
Variation increases. In the first embodiment, the injection timing (injection start timing) of the multiple injection is fixed to a predetermined timing during the intake stroke. In step S17, multiple injections for injecting the required injection amount (injection time) in the total injection period by dividing the number of injections into the total number of injections are started at the fixed injection timing (injection start timing). The mixture is compressed and self-ignited near TDC.

When the multiple injection is performed, as shown in FIG. 9, the air-fuel mixture in the combustion chamber has an irregular air-fuel ratio variation, and the air-fuel mixture having the irregular air-fuel ratio variation has a rich air-fuel ratio. Compression self-ignition combustion will be started from that portion. In the case of compression self-ignition combustion, as shown in FIG. 10, when the air-fuel ratio is made lean, the combustion stability is deteriorated, and when the air-fuel ratio is made rich, the knocking strength is increased, and the combustion stability can be made within an allowable range. Lean limit air-fuel ratio AFL
It is necessary to control the air-fuel ratio in a narrow range between the air-fuel ratio and the rich limit air-fuel ratio AFR that can suppress the knocking strength within an allowable range. Is difficult.

In FIG. 10, the air-fuel ratio is used as an index indicating the ratio between gas and fuel. However, the same tendency is shown when residual gas or recirculated exhaust gas is contained. It is the ratio of the total gas amount, which is the sum of fresh air and burned gas, to the fuel. Therefore, as a method of securing combustion stability while promoting lean operation, stratification of an air-fuel mixture that forms a rich air-fuel mixture in a part of the combustion chamber can be considered. However, combustion of the rich air-fuel mixture causes a large NOx emission. turn into.

On the other hand, if the air-fuel ratio is irregularly varied by the multiple injections as described above, the air-fuel ratio is made leaner while suppressing an increase in the amount of NOx emission, and the compression self-fuel ratio is increased. The ignition combustion area can be expanded to the low load side. When the multiple injection is performed, as described above, an irregular air-fuel ratio variation occurs in the air-fuel mixture in the combustion chamber (see FIG. 9). However, when the required fuel amount is injected only once in the intake stroke (this embodiment). In the case of the spark ignition combustion in the embodiment, as shown in FIG. 11, a substantially uniform air-fuel ratio is formed in the combustion chamber, and the fuel is injected once in the compression stroke so that the vicinity of the ignition plug 9 is formed. In the case of performing stratification of the air-fuel mixture to form a rich air-fuel mixture in a local region, as shown in FIG.
An extremely lean mixture is formed by diffusion from the local area.

Therefore, the frequency distribution of the air-fuel ratio (equivalent ratio) in the air-fuel mixture formed by each of the intake stroke single injection (homogeneous), the multiple injection, and the compression stroke injection (stratified) is as shown in FIG. The variation of the air-fuel ratio (equivalent ratio) in the multiple injection is larger than in the single intake stroke injection and smaller than in the compression stroke injection. On the other hand, as the variation in the air-fuel ratio (equivalent ratio) increases, as shown in FIG. 14, the lean limit air-fuel ratio AFL (lean limit of the average air-fuel ratio) becomes leaner because the combustion stability is improved. If the variation exceeds a certain limit, the rich limit air-fuel ratio AFR (the rich limit of the average air-fuel ratio) becomes lean.

FIG. 15 shows the correlation between the variation in the air-fuel ratio (equivalent ratio) and the range in which the self-ignition combustion is established. As the variation in the air-fuel ratio increases, the range in which the self-ignition combustion is established becomes lower. However, if the variation in the air-fuel ratio becomes too large, the load limit of the rich limit is reduced, so that the range of the fuel cell becomes narrower. Here, the region where the rich limit sharply reduces the load is the air-fuel ratio variation region when stratification is performed by the compression stroke injection, and in the air-fuel ratio variation region due to multiple injections smaller than when stratification is performed, the rich limit is reduced. Without reducing the load on the vehicle, the range in which the self-ignition combustion is established can be expanded to the low load side.

FIG. 16 shows the correlation between the variation of the air-fuel ratio (equivalent ratio) and the HC / NOx emission.
If the air-fuel ratio variation becomes too large, the NOx emission increases, but in a region smaller than the air-fuel ratio variation region in which the NOx emission tends to increase, both the HC emission and the NOx emission do not change. As shown in FIGS. 15 and 16, when stratification is achieved, the load in the range in which the compression self-ignition combustion is established can be reduced, but the NOx emission increases.

On the other hand, when an irregular air-fuel ratio variation is set, without increasing the NOx emission amount,
The range in which the compression self-ignition combustion is established can be reduced, and in the present embodiment, the compression self-ignition combustion is performed by setting an irregular air-fuel ratio variation in the air-fuel mixture by multiple injections.
The low-load side, which does not fall within the range of self-ignition combustion with a homogeneous mixture, is included in the compression auto-ignition combustion region, and NOx
An increase in emissions can be avoided.

Further, in the above embodiment, the magnitude of the variation in the air-fuel ratio given to the air-fuel mixture by the multiple injection is controlled by the number of injections and the total injection period. The ignitability in the compression self-ignition combustion tends to deteriorate as the engine speed increases and the engine load decreases, while the combustion stability improves as the air-fuel ratio variation increases.

Further, as the number of injections in the multiple injection increases, and as the total injection period in the multiple injection increases, the air-fuel ratio variation increases (see FIGS. 6 and 8). Therefore, in the present embodiment, as described above, the higher the engine speed and the lower the engine load, the greater the number of injections and the longer the total injection period.

Incidentally, one of the number of injections and the total injection period may be fixed, and the other may be changed according to the engine speed and the engine load. By the way, in the first embodiment, the injection start timing of the multiple injections is fixed, and the air-fuel ratio variation is controlled by the number of injections and the total injection period. A configuration for controlling the fuel ratio variation may be employed, and a second embodiment having such a configuration will be described with reference to the flowchart of FIG.

The flow chart of FIG.
6, the injection timing (injection start timing) is set in step S27, and step S2 is performed.
In step 8, multiple injections of the set total injection period and injection number are started at the start timing set in step S27. Note that each step other than the above is performed
Since the same processing as in the flowchart of FIG. 3 is performed, the description is omitted.

In step S27, as shown in FIG. 18, the higher the engine speed and the lower the engine load,
A setting is made to further retard the injection start timing of the multiple injection.
This is because the higher the engine rotation speed and the lower the engine load, the worse the ignitability becomes. On the other hand, as shown in FIG. 19, the more the injection start timing of the multiple injection is retarded, the more the air-fuel ratio (equivalent ratio).
This is because the variation in 大 き く increases and the ignition stability is improved.

The air-fuel ratio variation may be controlled by changing only the injection start timing, or the air-fuel ratio may be varied by setting one of the total injection period and the number of injections and the injection start timing variably. A configuration for controlling the variation may be adopted. By the way, in the above embodiment, the air-fuel mixture having the irregular air-fuel ratio variation formed by the multiple injection is configured to be compressed and self-ignited and burned by itself, but the irregular air-fuel ratio which does not lead to the self-ignition by itself is adopted. A mixed gas field having variation (hereinafter, referred to as a main gas mixture field) is formed by multiple injections, and an additional temperature rise is applied to the main gas mixture field to execute a combustion mode that leads to self-ignition combustion. The third embodiment will be described below.

FIG. 20 shows the injection control in the third embodiment. If it is determined in step S32 that the engine is in the compression self-ignition combustion region, the total injection period and injection in the multiple injection are determined in steps S35 to S37. The number of times and the injection start timing are set as in the second embodiment. Step S3
At step 8, as shown in FIG. 21, it is determined whether or not the compression self-ignition combustion region is the two-stage combustion region set on the high load / high rotation side or the other one-stage combustion region.

The first-stage combustion region is a combustion in which the air-fuel mixture having an irregular air-fuel ratio variation formed by the multiple injections is self-ignited and burns by itself. In the same manner as described above, the mixture formed by the multiple injection (main mixture field) is a combustion mode in which heat is generated by the combustion of the fuel additionally injected after the multiple injection, thereby leading to self-ignition combustion. Since combustion is performed twice, that is, combustion that triggers self-ignition combustion and subsequent combustion in the main air-fuel mixture field, it is referred to as two-stage combustion (see FIG. 22).

If it is determined in step S38 that the fuel is in the first-stage injection region, the process proceeds to step S39, in which the amount of fuel that reaches autoignition combustion near the compression top dead center is reduced by the total injection period,
Injection is performed by multiple injections according to the setting of the number of injections and the injection start timing. On the other hand, if it is determined in step S38 that it is in the two-stage combustion region, the process proceeds to step S40, in which multiple injections are performed according to the settings of the total injection period, the number of injections, and the injection start timing. A fuel quantity that does not start self-ignition combustion before is injected in multiple injections to form a main mixed gas field that is premixed by the time of trigger combustion.

In the next step S41, the aforementioned step S41
An additional fuel injection is performed once near the top dead center after the multiple injections at 40, thereby forming a rich mixture in a local region immediately below the fuel injection valve 8 and stratifying the mixture (FIG. 2).
3). Fuel injected near the top dead center is:
It is the minimum amount to start compression self-ignition combustion,
When the fuel injected near the top dead center is compressed self-ignition combustion, the heat generated by the combustion causes the main mixture field to be compressed self-ignition combustion.

According to the above configuration, even in the case of performing two-stage combustion, since the main air-fuel mixture field has an irregular air-fuel ratio variation and thus has good ignitability, the local air-fuel mixture has a high ignitability. The amount of fuel can be reduced, and the emission of NOx due to combustion of the rich mixture can be suppressed. Furthermore, by adopting a configuration in which two-stage combustion is performed, the rate of rise of the in-cylinder pressure can be suppressed to prevent occurrence of knocking, so that compression self-ignition combustion is achieved on a higher load side than in the case of performing one-stage combustion. Can be done.

In the above description, the local rich air-fuel mixture is compressed and self-ignited. However, the local rich air-fuel mixture is burned by spark ignition by the spark plug 9, and the main mixture is generated by the heat generated by the combustion. It is good also as composition which brings an air field to compression self-ignition combustion. In the above embodiments, the air-fuel ratio variation required from the engine rotation speed and the engine load is mapped in advance, and the total injection period, the number of injections, and the injection start timing correlated with the air-fuel ratio variation are feedforward controlled according to the map. Although the knocking intensity and the combustion stability are detected, the air-fuel ratio variation (total injection period, number of injections, injection start timing) may be feedback-controlled so that these values become allowable values. The fourth embodiment will be described with reference to the flowchart of FIG.

In the compression self-ignition combustion region, the total injection period, the number of injections, and the injection start timing are set based on the engine speed and the engine load, and multiple injections are performed based on the settings. The formation of the air-fuel mixture (steps S45 to S48) is the same as in the second embodiment. In step S49, knocking strength and combustion stability are detected.

As shown in FIG. 1, the knocking intensity is detected based on a detection signal from a knock sensor (vibration sensor) 11 provided in the cylinder block. In addition, the combustion stability is determined based on a detection signal of the crank angle sensor 10 to determine an engine rotation fluctuation, and is determined based on the rotation fluctuation. In step S50, it is determined whether the detected knocking intensity and the combustion stability are both within allowable values, both are not within allowable values, or one is within allowable values and the other is not within allowable values.

If both the knocking strength and the combustion stability are not within the allowable values, there is no compression self-ignition combustion range. At this time, the mode is switched from compression self-ignition combustion to spark ignition combustion. When both the knocking intensity and the combustion stability are within the allowable values, the process proceeds to step S51, in which the air-fuel ratio variation of the air-fuel mixture formed by the multiple injection is reduced, so that the compression auto-ignition combustion is performed with a minimum required variation. Let it be established.

The correction for reducing the variation in the air-fuel ratio is performed by advancing the injection start timing of the multiple injection. However, the air-fuel ratio variation may be reduced by shortening the total injection period or reducing the number of injections,
A configuration may be used in which two or more of the advance correction of the injection start timing, the shortening correction of the total injection period, and the reduction correction of the number of injections are combined.

Further, if one of the states is within the allowable value (OK) and the other is not within the allowable value (NG), step S
Proceeding to 52, it is determined whether or not the knocking intensity is within an allowable value (OK). When the knocking intensity is not within the allowable value (NG), that is, when the combustion stability is within the allowable value (OK) but the knocking intensity is higher than the allowable value, the process proceeds to step S51, and the multiplexing is performed. The air-fuel ratio variation of the air-fuel mixture formed by the injection is reduced.

On the other hand, the knocking strength is within the allowable value (OK).
, That is, the combustion stability is not within the allowable value (N
If the state is G), the process proceeds to step S53, in which the air-fuel ratio variation of the air-fuel mixture formed by the multiple injection is increased and corrected. The correction for increasing the variation in the air-fuel ratio is performed by delaying the injection start timing of the multiple injection. However, the air-fuel ratio variation may be increased by increasing the total injection period or increasing the number of injections. Alternatively, the increase in the injection start timing, the increase in the total injection period, or the increase in the number of injections may be performed. It is good also as a structure which combines two or more.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an internal combustion engine according to an embodiment.

FIG. 2 is a diagram showing a self-ignition combustion region and a spark ignition combustion region in the embodiment.

FIG. 3 is a flowchart illustrating fuel injection control according to the first embodiment.

FIG. 4 is a view showing a pattern of an injection signal during multiple injection control.

FIG. 5 is a diagram showing a correlation between a total injection period and an engine load / rotation in multiple injection.

FIG. 6 is a diagram showing a correlation between a total injection period and air-fuel ratio variation in multiple injection.

FIG. 7 is a diagram showing a correlation between the number of injections and the engine load / rotation in multiple injections.

FIG. 8 is a diagram showing a correlation between the number of injections and air-fuel ratio variation in multiple injections.

FIG. 9 is a view showing an air-fuel ratio variation of an air-fuel mixture formed by multiple injections.

FIG. 10 is a diagram showing a correlation between an air-fuel ratio and knocking strength, combustion stability, and combustion timing.

FIG. 11 is a diagram showing an air-fuel ratio variation of an air-fuel mixture formed by a single injection in an intake stroke.

FIG. 12 is a diagram showing a variation in air-fuel ratio when stratification is performed by compression stroke injection.

FIG. 13 is a diagram showing a frequency distribution of the air-fuel ratio in the air-fuel mixture formed by the multiple injection, the intake stroke single injection, and the compression stroke injection.

FIG. 14 is a diagram showing a correlation between an air-fuel ratio and a rich / lean limit air-fuel ratio.

FIG. 15 is a diagram showing a correlation between an air-fuel ratio variation and a range in which compressed self-ignition combustion is established.

FIG. 16 is a diagram showing a correlation between air-fuel ratio variation and NOx / HC emissions.

FIG. 17 is a flowchart illustrating fuel injection control according to the second embodiment.

FIG. 18 shows injection start timing and engine load in multiple injection.
FIG. 4 is a diagram showing a correlation with rotation.

FIG. 19 is a diagram showing a correlation between an injection start period and air-fuel ratio variation in multiple injection.

FIG. 20 is a flowchart illustrating fuel injection control according to a third embodiment.

FIG. 21 is a diagram showing a spark ignition combustion region and a compression self-ignition combustion region including a first-stage fuel region and a second-stage combustion region in the third embodiment.

FIG. 22 is a diagram showing a change in in-cylinder pressure during two-stage combustion in the third embodiment.

FIG. 23 is a view showing an air-fuel ratio variation of an air-fuel mixture formed in a two-stage combustion region.

FIG. 24 is a flowchart illustrating fuel injection control according to a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Intake port 4 ... Intake valve 5 ... Exhaust port 6 ... Exhaust valve 7 ... Cylinder head 8 ... Fuel injection valve 9 ... Spark plug 10 ... Crank angle sensor 11 ... Knock sensor 20 ... Engine control unit (ECU) 21: combustion pattern determination unit 22: spark ignition combustion control unit 23: self-ignition combustion control unit 24: injection number control unit 25: injection period control unit 26: injection timing control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/40 F02D 41/40 F 45/00 312 45/00 312N 312J 345 345B 368 368B F02P 17/12 F02P 17/00 R (72) Inventor Akihiko Tsunokata 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Nissan Motor Co., Ltd. (reference) 3G019 AA01 AB02 AB03 AC03 GA01 GA05 GA09 GA14 3G084 AA00 BA09 BA11 BA13 BA15 BA16 CA03 CA09 DA10 DA38 EA07 EB09 EC01 EC03 FA10 FA18 FA25 FA33 FA38 3G301 HA01 HA04 JA22 JA25 KA06 KA08 KA23 MA01 MA11 MA18 MA26 MA27 NC04 NE23 PA11Z PA17Z PC08Z PE01Z PE03Z

Claims (10)

[Claims] 1. A combustion control device for an internal combustion engine that performs a compression self-ignition combustion operation, wherein an irregular air-fuel ratio variation is provided in an air-fuel mixture in a combustion chamber during the compression self-ignition combustion operation. Engine combustion control device. 2. A combustion control device for an internal combustion engine that performs a compression self-ignition combustion operation, wherein during a compression self-ignition combustion operation, an additional temperature rise is applied to a main air-fuel mixture field to reach a compression self-ignition combustion. A combustion control apparatus for an internal combustion engine, wherein the main mixture field has irregular air-fuel ratio variations. 3. A fuel injection valve for directly injecting fuel into a cylinder, wherein after the fuel injection forming the main mixture field,
Additional fuel injection is performed to form a local rich mixture field, and the main mixture field is compressed and self-ignited by a temperature increase due to spark ignition combustion or compression self-ignition combustion of the local rich mixture field. 3. The combustion control device for an internal combustion engine according to claim 2, wherein the combustion is performed. 4. The air-fuel ratio variation increases as the rotational speed of the engine increases.
The combustion control device for an internal combustion engine according to any one of the above. 5. The combustion control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio variation increases as the engine load decreases. 6. The engine according to claim 1, wherein the combustion stability and the knocking intensity of the engine are detected, and the air-fuel ratio variation is controlled so that the combustion stability and the knocking intensity of the engine fall within allowable ranges, respectively. The combustion control device for an internal combustion engine according to any one of claims 1 to 3. 7. A fuel injection valve for directly injecting fuel into a cylinder, wherein the fuel-air mixture having the irregular air-fuel ratio variation is periodically divided into two or more times in one cycle by dividing the fuel. 7. The combustion control device for an internal combustion engine according to claim 1, wherein the combustion control device is formed by multiple injections. 8. A combustion control apparatus for an internal combustion engine according to claim 7, wherein said air-fuel ratio variation is controlled by the number of injections of said multiple injections. 9. The combustion control device for an internal combustion engine according to claim 7, wherein the air-fuel ratio variation is controlled by a period during which the multiple injection is performed. 10. The air-fuel ratio variation is controlled by the injection timing of the multiple injection.
The combustion control device for an internal combustion engine according to any one of the above.