JP2002115593A - Combustion control apparatus for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To distribute fuel to an appropriate position in an appropriate degree of concentration in a combustion chamber by properly carrying out split injection of fuel. SOLUTION: Required amount of fuel injection under the condition of injecting the fuel in a compression stroke, is injected by split injection in which the fuel is injected in plural fuel injection periods constituting an initial spray (small spray angle and high spray speed) and a main spray (large spray angle and low spray speed) in the compression stroke. The condition for the split injection is set depending on the operating condition(the number of split injections N (2 in the figure), the injection start period τ 12 and the proportion of fuel injection amount, or the like).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control system for an internal combustion engine, and more particularly to a combustion control system for a direct injection spark ignition type internal combustion engine which divides a compression stroke fuel injection during a stratified charge combustion operation into a plurality of injections. And a technique for obtaining a spray form.

[0002]

2. Description of the Related Art As a conventional split fuel injection technique in a direct injection spark ignition type internal combustion engine, at least two injections are performed during stratified charge combustion operation at low engine speed and low load operation, and the fuel injected earlier is used. A uniform air-fuel mixture is formed in the combustion chamber, and the intensive air-fuel mixture formed by the fuel injected later is ignited at the timing of passing near the spark plug, thereby improving combustion stability. On the other hand, a technique for preventing the generation of unburned hydrocarbons (HC) due to insufficient mixing of fuel and air is known (see Japanese Patent Application Laid-Open No. 9-256936).

[0003]

However, in such a split injection, although effects such as improvement of combustion stability and reduction of the amount of HC generated can be obtained in a part of the operation region, the following specific operation is performed. There is a problem in the area. That is, in the past, previously injected fuel diffused throughout the combustion chamber to form a lean homogeneous mixture.
During low engine load operation with a small amount of fuel injection, the fuel injected earlier may form an excessively lean air-fuel mixture, resulting in incomplete combustion, which may instead increase the amount of HC generated.

[0004] Further, in the case of performing the above-described conventional split injection in a direct injection spark ignition type internal combustion engine in which the air-fuel mixture is transported to the vicinity of a spark plug by carrying the air-fuel mixture on a tumble flow of the intake air, Problems arise. That is, when the engine is running at a low speed where the air-fuel mixture is hardly transported with the intake air momentum being relatively small with respect to the spray momentum and the air-fuel mixture is hardly transported, or when the fuel injection amount is small and the air-fuel mixture tends to be lean. During the operation, the period during which the mixture of the appropriate concentration exists near the spark plug, that is, the ignitable period is limited. In such an operation region, it is difficult to extend the ignitable period, and as a result, the ignitable period becomes insufficient in engine performance, and the combustion stability is reduced.

In view of such circumstances, the present invention distributes fuel to appropriate positions and at appropriate concentrations by performing divided injection of fuel more accurately, and allows the ignition period to extend over the entire operating region. An object of the present invention is to provide a combustion control device for an internal combustion engine that can be sufficiently secured.

[0006]

Therefore, a combustion control apparatus for an internal combustion engine E according to the present invention includes a fuel injection valve for directly injecting fuel into a combustion chamber, and a spark plug, and supplies fuel at least in a compression stroke. A combustion control device for an internal combustion engine having operating conditions for injecting, as shown in FIG. 1, a fuel injection amount required for injecting fuel in a compression stroke with respect to the fuel injection valve, in a compression stroke, Divided into a plurality of injection periods in which the injection characteristics of the fuel injection valve are substantially equal,
It is characterized by comprising split injection control means for performing injection (claim 1).

[0007] The divided injection control means injects the previously injected fuel among the divided and injected fuel such that the subsequently injected fuel overlaps near the spark plug. Is preferable (claim 2). Further, the combustion control device for the internal combustion engine E according to the present invention may be configured to ignite the spark plug when the previously injected fuel and the subsequently injected fuel overlap each other near the spark plug. It is preferable to provide timing control means (claim 3).

It is preferable that the split injection control means makes at least one of an injection start interval and an injection amount ratio variable according to operating conditions. In this case, the split injection control means preferably extends the injection start interval in accordance with the decrease in the engine speed (Claim 5). It is preferable to increase the injection amount ratio (claim 6), and to reduce the engine load, it is preferable to reduce the injection amount per injection while keeping the injection start interval substantially constant (claim 7). It is preferable to increase the ratio of the final injection amount to the total injection amount according to the decrease in the engine load.

Further, the combustion control apparatus for the internal combustion engine E according to the present invention preferably includes a division number setting means for setting the number of divisions in accordance with an operating condition with respect to the division injection control means. ). The split injection control means sets the required fuel injection amount to 1 under the condition that the injection suspension period between the injection periods is shorter than the shortest valve closing period of the fuel injection valve.
It is preferable that the fuel be injected by two injections.
0) It is preferable to detect this condition as a high-speed and high-load operation condition of the internal combustion engine E (claim 11).

In the case where three or more divided injections are performed, the divided injection control means preferably performs the injection with a shorter injection start interval from the immediately preceding injection as the later injection is performed.
2). Further, the combustion control device for the internal combustion engine E according to the present invention comprises an engine temperature detecting means and a split injection prohibiting means for receiving an output from the means and for prohibiting split fuel injection by the split injection control means when the engine is cold. (Claim 13).

[0011]

According to the first aspect of the present invention, the required fuel injection amount in the case of injecting fuel in the compression stroke is divided by the divided injection control means with injection characteristics equal to a plurality of injection periods in the compression stroke. The following effects can be obtained by jetting. Among the split fuels, the fuel injected first forms an air-fuel mixture in a region determined by the injection characteristics of the fuel injection valve, the injection direction, the influence of the gas flow in the combustion chamber, and the like. Then, for fuel injected with the same injection characteristics after this injection, a flow along the injection direction occurs due to the influence of the previous injection, so that the fuel injected later has a similar form of spray. While forming, it travels through the combustion chamber at a higher speed than the previously injected fuel. Therefore, by causing the fuel injected later to catch up with the fuel injected earlier and overlap, it is possible to form an air-fuel mixture having an appropriate concentration at that position.

According to the second aspect of the present invention, the mixture having the appropriate concentration can be formed in the vicinity of the spark plug. The possible period can be sufficiently secured, and the combustion stability can be improved. Further, it is possible to prevent the formation of an excessively lean air-fuel mixture, and to achieve both improvement in combustion stability and reduction in the amount of generated HC.

According to the third aspect of the invention, the ignition timing is optimized by the ignition timing control means. Claim 4
According to the present invention, the position at which the divided fuels overlap and the degree of concentration of the fuel at that position can always be kept good regardless of the operating conditions.

According to the fifth aspect of the present invention, it is possible to suppress a change in a position where overlapping of the divided fuels occurs with respect to a change in the engine speed. In particular, when the fuel is transported toward the ignition plug on the tumble flow of the intake air, the tumble flow is weakened, and even during the engine low-speed operation where the fuel is less likely to be transported, the divided injection is performed. The position where the fuel overlaps is maintained near the spark plug, and the ignitable period can be secured.

According to the invention of claim 6, the following effects can be obtained. Since the fuel injected later overlaps the fuel injected earlier without being dispersed relatively, if the injection amount ratio is increased as the fuel is injected later, the fuel concentration of the spray formed by the fuel overlap is increased. Can be increased. Therefore, for example, during low-speed engine operation when fuel is transported toward the ignition plug by being carried on the tumble flow of intake air, by increasing the final injection amount ratio, ignition is performed under conditions where combustion stability tends to decrease. The concentration of fuel near the plug can be increased, and the combustion stability can be improved.

According to the seventh aspect of the invention, the injection start interval is kept substantially constant with respect to the decrease in the engine load, so that the position where the overlapped fuels are overlapped can be targeted as desired regardless of the engine load. It is possible to keep the fuel concentration at that position, and to prevent a decrease in the concentration of fuel at that position. When the fuel is transported toward the spark plug by taking the tumble flow of the intake air, the required fuel injection amount is small, and even at the time of engine low load operation in which the air-fuel mixture tends to be lean, the fuel in the vicinity of the spark plug is It is possible to maintain the concentration of fuel and secure the ignitable period.

According to the invention of claim 8, the following effects can be obtained. As described above, by increasing the injection amount ratio in the later injection, the fuel concentration of the spray formed by overlapping of the fuel can be increased. Therefore, in the case where the air-fuel mixture is formed intensively in the vicinity of the spark plug, the required fuel injection amount is small, and even during the engine low-load operation in which a lean air-fuel mixture is easily formed, the final injection amount ratio is reduced. By increasing, the concentration of fuel in the vicinity of the spark plug can be made good, the formation of a lean mixture can be suppressed, and the ignitable period can be secured.

According to the ninth aspect of the present invention, the division number setting means can inject the fuel in an optimum number according to the operating conditions. According to the tenth aspect, it is possible to reliably inject the required fuel injection amount and prevent load fluctuation. According to the eleventh aspect, it is possible to prevent load fluctuations under high rotation and high load operation conditions.

According to the twelfth aspect of the present invention, it is possible to overlap fuels split and injected at appropriate positions and to further increase the fuel concentration of the spray formed by the overlap. That is, as described above, fuel overlap occurs without being dispersed as much as fuel injected later. However, the required fuel injection amount is divided into three injections, and the later injection is performed from the injection immediately before the injection. By shortening the injection start interval, the dispersion of the fuel injected later is further suppressed, and the fuel concentration of the spray due to the overlap can be further increased. Further, the distribution range of fuel and the degree of concentration thereof can be made more favorable under conditions where the combustion stability is likely to be reduced, and the combustion stability can be further improved.

According to the thirteenth aspect of the present invention, even when the engine wall surface temperature is high and the fuel wall surface adheres, the split injection is performed only at the time of the engine temperature where the adverse effect on the combustion performance is small. Since the split injection can be prohibited, it is possible to prevent the deterioration of the combustion performance due to the adhesion of the fuel to the wall surface.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment of the present invention, the present invention is applied to a four-cycle type automobile gasoline engine (hereinafter simply referred to as "engine") E which is a direct injection spark ignition type internal combustion engine. An example of application will be described with reference to the drawings. FIG. 2 is a side sectional view of the engine E,
This shows the state of the compression stroke. In the figure, 1 is a cylinder block, 2 is a cylinder head, and a piston 3 forming a concave crown surface is inserted into the cylinder block 1. Then, a combustion chamber 4 is formed between the crown surface of the piston 3 and the cylinder head 2.

The combustion chamber 4 has an intake port 5 on one side and an exhaust port 6 on the other side, and each port is opened and closed by an intake valve 7 or an exhaust valve 8 interposed respectively. It should be noted that two intake ports 5 and two exhaust ports 6 are provided. An ignition plug 9 is attached to the cylinder head 2 so as to be located substantially at the center of the upper side of the combustion chamber 4, and is further positioned lower between the two intake ports 5 and 5 for fuel injection. A valve 10 is mounted. The fuel injection valve 10 is capable of directly injecting fuel into the combustion chamber 4 and injects fuel obliquely downward toward the lower side of the ignition plug 9 as shown by a dashed line A in the figure.

Here, in the combustion chamber 4, a tumble (longitudinal vortex) flow of intake air is formed during the intake stroke by the action of the shape of the intake port 5, and when performing stratified combustion, the fuel injection valve is used. 10 injects fuel in the compression stroke. The injected fuel is transported in the combustion chamber 4 in the direction of the ignition plug 9 along the tumble flow. As a result, a mixture having a combustible air-fuel ratio is formed near the ignition plug 9, and the mixture in the combustion chamber 4 is mixed. Qi is stratified.

Next, the formation of an air-fuel mixture in the engine E according to the present embodiment will be further described with reference to FIGS. First, referring to FIGS. 3 and 4, a spray form of fuel injected by the fuel injection valve 10 will be described. FIG. 3 shows an example of the spray form, and FIG. 4 shows changes in the spray angle α and the spray speed v with respect to the elapsed time from the injection start time t0.

In the present embodiment, the fuel injected once by the fuel injection valve 10 in the compression stroke is shown in FIGS.
As shown in (2), the spray is formed from an initial spray at the beginning of the injection start (the spray angle α is small and the spray speed v is high), and a subsequent main spray (the spray angle α is large and the spray speed v is low).
Together, these form a substantially spherical spray having a spray length L.

Under the operating condition of injecting fuel in the compression stroke, as shown in the time chart of FIG. 5, the fuel injection valve 10 determines the required fuel injection amount to be injected under the condition, and the injection characteristics of the fuel injection valve 10 are equal. The fuel injection is divided into a plurality of injection periods each having a predetermined length, that is, such that each fuel spray includes the initial spray and the main spray (accordingly, each injection period is based on the initial spray periods t0 to t1 shown in FIG. 4). Long.) Divide into multiple sprays and spray. Here, an example is shown in which the injection is divided into two injection periods τ1 and τ2.

Here, FIG. 5 will be further described. Naturally, when the fuel is divided into several injections, the injection amount per injection is equal to the single injection amount when the required fuel injection amount is injected by only one injection. In comparison, it decreases. Here, referring to FIG. 6, which shows the spray tip reaching distance for each injection amount, the tip reaching distance of the fuel spray by the first injection related to the split injection is the spray tip reaching distance in the case of only one injection. Lower than the distance.

On the other hand, the fuel spray by the second injection, which is performed with a slight injection suspension period from the end of the first injection, is caused by the gas flow in the injection direction formed by the first injection. Since the vehicle rides and travels in the combustion chamber 4, the spray speed becomes higher than the fuel spray by the first injection. Therefore, the fuel spray from the second injection catches up with the fuel spray from the first injection (St).
4) At a specific timing, the sprays are exactly overlapped to form a composite spray having a short length (St).
5). Then, the tip of the second spray overtakes the tip of the first spray and reaches farther than the first spray (St6).

The composite spray formed by injecting the required fuel injection amount in a plurality of times in this manner is more compact than the spray by only one injection, and The fuel can be more concentrated and distributed in the section. Further, the fuel injection start interval τ12
By setting the injection conditions such as the ratio of the injection amount per injection to the total injection amount variably according to the operating conditions (for example, the engine speed and the engine load), the position where a plurality of sprays overlap, The fuel concentration can always be kept optimal.

Since the injected fuel is transported in the direction of the spark plug 9 on the tumble flow of the intake air, the above-mentioned overlap can be generated near the spark plug 9. By forming a composite spray in the vicinity of the ignition plug 9 in this manner, it is possible to improve the mixture formation in performing stratified combustion and improve the combustion stability.

FIG. 7 shows the variation of the air-fuel ratio in the vicinity of the spark plug 9 in the case of single injection (indicated by a dotted line) and in the case of double injection (indicated by a solid line). Referring to the figure, it can be seen that the period in which the air-fuel ratio in the vicinity of the ignition plug 9 is within an appropriate range (ignition possible period) is longer than in the case of single injection. Next, the control content for forming the air-fuel mixture described above will be described.

Here, the configuration of the control system will be briefly described with reference to FIG. Spark plug 9, fuel injection valve 10
And a fuel pump 31 for supplying fuel thereto at a high pressure is controlled by an engine control unit (hereinafter referred to as “ECU”) 21.
The ECU 21 receives a well-known crank angle sensor 41, a cylinder discrimination sensor 42, a throttle sensor 43, and an intake air amount sensor 4.
4. Signals from the fuel pressure sensor 45, the air-fuel ratio sensor 46, the water temperature sensor 47, and the like are input.

The ECU 21 controls fuel injection and ignition based on signals from these various sensors. The fuel injection calculates a fuel injection amount according to the engine speed and the engine load, and generates a required fuel pressure by the fuel pump 31.
The fuel injection valve 10 issues an injection command as an injection pulse signal.
Is performed. The ignition is performed by driving an ignition coil (not shown) by the ignition signal to discharge the ignition plug 9.

FIG. 8 is a flowchart of control (mainly fuel injection control) during stratified combustion operation in which fuel is injected during the compression stroke. Hereinafter, description will be made with reference to FIG. In step (hereinafter abbreviated as "S") 1, an operating state is detected. That is, the engine speed, the engine load, the cooling water temperature, and the like are detected based on the signal from the sensor.

In S2, the optimum fuel injection amount (required fuel injection amount) for the detected operating state is calculated. This calculation is
The calculation may be performed using a theoretical calculation formula or a map. In S3, based on the calculated required fuel injection amount and the fuel pressure detected by the fuel pressure sensor 45, the injection pulse signal width (the entire injection period, and the pulse width in the case of only one injection, (In the case of split injection, this corresponds to the total width of each pulse.) Τ is calculated.

In S4, it is determined from the cooling water temperature (engine wall temperature) whether or not the engine is in a cold state. If the engine is in a cold state, the process proceeds to S8, otherwise (in an engine warm state). Is S5
Proceed to. Although the control in S8 will be further described later, when the engine is cold, the engine wall temperature is low and the fuel wall adhesion has a large adverse effect on the combustion performance, so the split injection is prohibited and the single injection is performed only once. The injection is performed from the injection start timing set in S8. Therefore, S4 is
This constitutes split injection prohibition means.

In S5, an injection mode for determining whether injection is performed only once or split injection is determined with reference to a tendency map as shown in FIG. The injection mode is set for each region corresponding to the engine speed and the engine load, and the low-speed low-load operation condition (region A) for performing the stratified combustion operation.
In 1 and A2), compression stroke injection is performed. Among them, the split injection mode is selected particularly in the region A1 where the engine speed and the engine load are low, and the single injection mode is selected in the other regions A2. On the other hand, in the region B other than the regions A1 and A2, a single intake stroke injection (that is, a single injection mode) is performed.
And perform a homogeneous combustion operation. When the split injection mode is selected, the process proceeds to S6, and when the single injection mode is selected, the process proceeds to S8.

In step S6, the injection pulse signal width (full injection period) τ and the number of divisions N (here, 2) are used, and FIG.
The injection pulse signal widths τ1 and τ2 in each injection are calculated with reference to a map having a tendency as shown in FIG. In addition,
The map of FIG. 10 shows the final time (2
The optimum value of the injection amount ratio r of the second time is assigned according to the engine speed and the engine load, and is set to be larger as the rotation speed and the load become lower. Here, the ejection pulse signal widths τ1 and τ2 are τ1 = τ−τ2 and τ2 = τ × r.

The reason why the final injection amount is changed in accordance with the engine speed and the engine load is as follows. In general, fuel injected into a combustion chamber is dispersed (diffused) with the passage of time, and a lean mixture is formed around a stratified mixture, which is a main cause of HC emission. . In the case of performing the split injection, the fuel can be concentrated as described above.However, if the fuel is injected at the same interval, the dispersion can be suppressed by increasing the proportion of the fuel injected at the last time. Thus, the generation of a lean mixture can be suppressed.

Therefore, by increasing the ratio of the final injection amount during the low engine speed operation and the low engine load operation in which the combustion stability is apt to decrease, the concentration of fuel near the ignition plug 9 is further increased. It is possible to extend the existence time of the air-fuel mixture having an appropriate concentration in the vicinity of the ignition plug 9 and prevent a decrease in combustion stability. In S7, the injection start interval τ12 is set with reference to the tendency map shown in FIG. As shown, the injection start interval τ12 increases as the engine speed decreases. In other words, the injection start interval τ12 is increased as the intake air tumble flow becomes weaker and the injected fuel is less likely to be transported toward the ignition plug 9.

The injection amount of each injection is reduced in accordance with the decrease of the engine load, while the injection start interval τ12
As shown in the map of FIG. 11, if the engine rotational speed is constant, the position where the overlapping of the fuels split and injected occurs by keeping the engine load substantially constant even if the engine load changes. However, it is always arranged near the spark plug 9 irrespective of the engine load. As a result, even during the low engine load operation, the concentration of the fuel can be made good, and the ignition possible period can be secured.

In step S8, the injection start timings C1 and C2 are set using the injection start interval τ12 and the injection pulse signal width τ2 and referring to a map of the injection end timing Ce having a tendency as shown in FIG. . In the map of FIG. 12, the optimum value of the injection end timing Ce is assigned in accordance with the engine speed and the engine load, and the more the engine is operated at a lower speed and the engine is operated at a higher load, the more retarded the engine is. And each injection start timing is C1 = Ce−C (τ12) −C (τ
2) and C2 = Ce−C (τ2). Note that C (τ2) is the injection period τ2
(The same applies to other periods).

In S9, the ignition timing ADV is set with reference to a tendency map as shown in FIG. In the map of FIG. 13, the optimum value of the ignition timing ADV is assigned in accordance with the engine speed and the engine load.
As a result of setting the ignition timing ADV with reference to this map,
The ignition plug 9 operates at a timing when the plurality of sprays split and injected overlap near the ignition plug 9. Therefore,
S9 constitutes ignition timing control means.

As described above, the required fuel injection amount in the case of injecting fuel in the compression stroke is determined by determining the injection characteristic of the fuel injection valve 10, that is, the length of the fuel injection valve 10 in which the respective fuel sprays have substantially the same form. Multiple injection periods τ1 and τ2
And the fuel spray injected first is sprayed so that the fuel spray injected later overlaps the fuel spray injected earlier in the vicinity of the spark plug 9, so that the mixture formed near the spark plug 9 is formed. Raise the concentration of fuel
In addition to preventing the generation of an excessively lean air-fuel mixture around the combustible air-fuel mixture, it is necessary to sufficiently secure the existence time of the air-fuel mixture having an appropriate concentration in the vicinity of the ignition plug 9, that is, the ignition possible period, and to improve the combustion stability. it can.

Note that, of the steps in the flowchart shown in FIG. 8, the processing of S1 to S8 constitutes the divided injection control means, and the processing of S9 constitutes the ignition timing control means. FIG.
9 shows an injection mode determination map (corresponding to the map in FIG. 9 referred to in S5 described above) in fuel injection control as another embodiment of the present invention.

In this case, the injection mode is set for each region corresponding to the engine speed and the engine load as described above, and the low-speed low-load operation condition (region A1-2, A1-2) for performing the stratified combustion operation is performed.
In A1-3 and A2), compression stroke injection is performed, and in other conditions (region B), a single intake stroke injection (that is, single injection mode) is selected to perform homogeneous combustion operation.
Further, in the case of performing the stratified combustion operation, the split injection mode is selected particularly in the regions A1-2 and A1-3 where the engine speed and the engine load are low. In A1-3, a three-time injection mode in which the required fuel injection amount is divided into three times and injected is selected. In the other area A1-2, the two-time injection mode is selected.

In the area A2, a single compression stroke injection (ie, a single injection mode) is selected. FIG.
FIG. 5 is a diagram illustrating an injection period and an ignition timing when a three-time injection mode is selected, and a tip end reach distance of a spray of dividedly injected fuel with respect to a lapse of time.

Even in the three-time injection mode, the fuel injection valve 1
0 indicates that the required fuel injection amount (injection pulse signal width τ) is divided into a plurality of sprays having the same injection characteristics (each injection pulse signal width τ1 to τ3 is longer than the initial spray period t0 to t1 shown in FIG. 4). To inject. Here, the injection start intervals τ12 and τ23 are preferably set such that the later the injection, the shorter the time from the immediately preceding injection. That is, in the case of the triple injection mode, τ23 <τ12.

Since the previously injected fuel spray catches up with the subsequently injected fuel spray and overlaps, the first to third fuel injections overlap near the spark plug 9 and are overlapped. In this case, a complex spray having a shorter length and a higher degree of concentration can be formed as compared with the case where two injections are performed. It is needless to say that it is preferable to ignite the composite spray formed as described above.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a cross-sectional side view of a direct injection gasoline engine according to an embodiment of the present invention.

FIG. 3 is an enlarged view of a spray during fuel injection.

FIG. 4 is a diagram showing changes in the spray angle and the speed of the same spray.

FIG. 5 is a diagram illustrating an injection period and an ignition timing in the case of performing a split injection (double injection), and a reaching distance of a tip end of a fuel spray injected in a divided manner with respect to a lapse of time.

FIG. 6 is a diagram showing a relationship between a spray tip reaching distance and an injection amount.

FIG. 7 is a diagram showing a difference in an ignition possible period between a single injection and a double injection;

FIG. 8 is a flowchart of fuel injection control according to an embodiment of the present invention.

FIG. 9 is a diagram showing an example of a map for determining an injection mode.

FIG. 10 is a diagram showing a change tendency of the final injection amount ratio to the total fuel injection amount according to engine operating conditions.

FIG. 11 is a diagram showing a change tendency of an injection start interval according to engine operating conditions.

FIG. 12 is a diagram showing a change tendency of an injection end timing according to engine operating conditions.

FIG. 13 is a diagram showing a change tendency of an ignition timing according to an engine operating condition.

FIG. 14 is a view showing another example of a map for determining an injection mode.

FIG. 15 is a diagram showing an injection period and an ignition timing in the case of performing a divided injection (three-time injection), and a reaching distance of a tip end of a fuel spray injected in a divided manner with respect to a lapse of time.

[Explanation of symbols]

 E ... Engine 1 ... Cylinder block 2 ... Cylinder head 3 ... Piston 4 ... Combustion chamber 5 ... Intake port 6 ... Exhaust port 9 ... Spark plug 10 ... Fuel injection valve 21 ... Engine control unit 31 ... Fuel pump

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Kenmei Kubo, 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside Nissan Motor Co., Ltd. Term (reference) 3G022 AA07 EA00 GA05 GA06 GA08 GA09 3G023 AA00 AA01 AA04 AB03 AC05 AD01 AD06 AD29 AG01 3G301 HA01 HA04 HA16 JA26 KA09 KA25 LB04 MA11 MA18 MA26 PA01Z PA11Z PB08Z PD03Z PE01Z PE03Z PE05Z PE08

Claims (13)

[Claims] 1. A combustion control device for an internal combustion engine, comprising: a fuel injection valve for directly injecting fuel into a combustion chamber; and a spark plug, and having an operating condition for injecting fuel at least in a compression stroke. In contrast, divided injection control means for dividing a required fuel injection amount in the case of injecting fuel in the compression stroke into a plurality of injection periods in which the injection characteristics of the fuel injection valve are substantially equal in the compression stroke, and injecting the divided injection periods. A combustion control device for an internal combustion engine, comprising: 2. The split injection control means according to claim 1, wherein said divided fuel is injected in such a manner that fuel injected later is overlapped with fuel injected earlier in the vicinity of said spark plug. The combustion control apparatus for an internal combustion engine according to claim 1, wherein the control is performed. 3. An ignition timing control means for igniting the spark plug when the previously injected fuel and the subsequently injected fuel overlap near the spark plug. The combustion control device for an internal combustion engine according to claim 2. 4. The apparatus according to claim 1, wherein said divided injection control means changes at least one of an injection start interval and an injection amount ratio according to operating conditions. Combustion control device for an internal combustion engine. 5. The combustion control apparatus for an internal combustion engine according to claim 4, wherein said split injection control means extends an injection start interval in accordance with a decrease in engine speed. 6. The combustion of an internal combustion engine according to claim 4, wherein said split injection control means increases the ratio of the final injection amount to the total injection amount in accordance with a decrease in the engine speed. Control device. 7. The fuel injection control device according to claim 4, wherein the split injection control means reduces the injection amount per injection while keeping the injection start interval substantially constant with respect to a decrease in engine load.
7. The combustion control device for an internal combustion engine according to any one of 6. 8. The apparatus according to claim 4, wherein said split injection control means increases the ratio of the final injection amount to the total injection amount in response to a decrease in engine load. A combustion control device for an internal combustion engine. 9. The internal combustion engine according to claim 1, wherein said split injection control means is provided with a split count setting means for setting a split count according to an operating condition. Engine combustion control device. 10. The split injection control means injects the required fuel injection amount by one injection under a condition that an injection suspension period between injection periods is shorter than a shortest valve closing period of the fuel injection valve. The combustion control device for an internal combustion engine according to any one of claims 1 to 9, wherein: 11. A combustion control apparatus for an internal combustion engine according to claim 10, wherein the condition that the injection suspension period becomes shorter than the shortest valve closing period is a high rotation and high load operation condition of the internal combustion engine. . 12. The split injection control means according to claim 1, wherein when performing three or more split injections, a later injection is performed with a shorter injection start interval from the immediately preceding injection. 12. The combustion control device for an internal combustion engine according to any one of 11. 13. An engine temperature detecting means and split injection prohibiting means for receiving an output from said means and prohibiting split fuel injection by said split injection control means when the engine is cold. 13. The combustion control device for an internal combustion engine according to any one of 1 to 12.