JP3820770B2 - In-cylinder direct injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder direct injection spark ignition engine.
[0002]
[Prior art]
In order to quickly activate the catalyst installed in the exhaust passage at the time of low temperature start, after performing the main injection in the intake stroke or the compression stroke, the sub injection in the expansion stroke or the exhaust stroke is subsequently performed ( JP-A-8-296485).
[0003]
In this case, a part of the sub-injection amount of fuel burns in the combustion chamber during the expansion stroke or exhaust stroke, and after being discharged into the exhaust passage, the temperature of the exhaust gas increases significantly or reaches the catalyst. Some of them burn afterwards, which causes the catalyst to rise in temperature early.
[0004]
[Problems to be solved by the invention]
By the way, when sub-injection is performed, an air-fuel ratio (hereinafter simply referred to as “total air-fuel ratio”) determined from the fuel of the sum of the main injection amount and the sub-injection amount per cycle (in a four-cylinder engine, a crank angle interval of 720 degrees). It is desirable that the air-fuel ratio be leaner than the stoichiometric air-fuel ratio (see Japanese Patent Application No. 10-205053).
[0005]
Accordingly, in order to make the total air-fuel ratio leaner than the stoichiometric air-fuel ratio at low temperature start when the main injection amount per cycle increases, the sub-injection amount per cycle must be relatively small. The minimum injection amount SR exists as a characteristic of the injection valve (see FIG. 10), and an injection amount below this cannot be set as one sub-injection amount for one cylinder, so the minimum injection amount SR is set to one sub-injection for one cylinder. If sub-injection is performed for all cylinders as the injection amount, the total air-fuel ratio may be richer than the stoichiometric air-fuel ratio. This is shown in FIG. 11, where the total air-fuel ratio is richer than the stoichiometric air-fuel ratio (indicated by stoichiometry in the figure) in the region where the cooling water temperature is below a predetermined value.
[0006]
As described above, when the total air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the amount of oxygen in the exhaust passage becomes insufficient, and not only HC and CO can be oxidized but discharged in a large amount, and also sufficient heat is generated by the oxidation reaction. Can no longer be expected.
[0007]
Therefore, the present invention provides a low temperature start by performing the sub-injection only in a limited number of cylinders at a low temperature start when the main injection amount per cycle is large and the sub-injection amount per cycle must be relatively small. The purpose is to prevent the total air-fuel ratio from becoming richer than the stoichiometric air-fuel ratio even at times.
[0008]
In addition, when performing sub-injection in the expansion stroke or exhaust stroke as in the conventional device, considering that the sub-injection amount may be extremely small, the cylinder that performs sub-injection is concentrated on one cylinder Is disclosed (see JP-A-9-112251). However, since this is one that performs sub-injection in order to supply HC as a reducing agent to the lean NOx catalyst, the sub-injection is always concentrated on one cylinder, and this is the catalyst as in the present invention. Even if it is intended to be used for the activation of the fuel, it is not always possible to use the sub-injection amount of fuel for efficient temperature rise.
[0009]
[Means for Solving the Problems]
The first invention relates to a direct injection type spark ignition engine in which direct injection is performed in an expansion stroke or an exhaust stroke after main injection is performed in an intake stroke or a compression stroke at a low temperature start. As shown, the means 31 for calculating the sub-injection amount F2 per cycle so that the total air-fuel ratio becomes the lean target value at the low temperature start, the sub-injection amount F2 per cycle and the fuel injection valve characteristics A means 32 for calculating the number N of sub-injection cylinders from the minimum injection amount SR, a means 33 for selecting a cylinder for performing sub-injection from the calculated number N of sub-injection cylinders, and only the selected cylinder under the condition for performing sub-injection. And means 34 for performing sub-injection.
[0010]
In the second invention, in the first invention, the number N of sub-injection cylinders is increased as the cooling water temperature rises or the time after start-up elapses.
[0011]
In the third invention, the cylinder that performs the sub-injection is selected so that the sub-injection is performed at equal intervals in one cycle section in the first or second invention.
[0012]
In the fourth invention, the sub-injection amount F2 per cycle is corrected so that the actual total air-fuel ratio in any one of the first to third inventions matches the lean target value.
[0013]
In the fifth invention, the difference between the actual total air-fuel ratio and the lean target value is stored as a learning value in any one of the first to third inventions, and the sub-injection amount per cycle at the next start is calculated. The stored learning value is used for correction.
[0014]
In a sixth aspect of the invention, the condition for performing sub-injection in any one of the first to fifth aspects of the present invention is set such that a parameter indicating a low temperature state at the time of starting (for example, a water temperature at starting, an oil temperature at starting) or after starting It is determined from parameters (for example, the elapsed time after starting, the cooling water temperature after starting) representing the engine warming-up state.
[0015]
In the seventh invention, in the sixth invention, when the starting water temperature is less than the predetermined value and the time after starting is less than the predetermined value, the sub-injection is not performed.
[0016]
【The invention's effect】
According to each of the first and sixth inventions, the sub-injection amount per cycle is calculated so that the total air-fuel ratio becomes the lean target value, and the sub-injection of one cylinder is calculated from the sub-injection amount per cycle. The number of sub-injection cylinders is calculated so that the amount is equal to or greater than the minimum injection amount, and sub-injection is performed only with a limited number of cylinders in one cycle, so the total air-fuel ratio is made lean even at low temperature start. be able to.
[0017]
Originally, sub-injection in all cylinders is more effective in increasing the oxidation reaction and exhaust temperature because mixing of oxygen, HC, and CO in the exhaust gas is promoted than in sub-injection in a limited number of cylinders. is there. Here, as the cooling water temperature rises or the time after start-up elapses, the combustion by the main injection becomes faster, and the main injection amount per cycle can be reduced accordingly, so that the sub-injection amount per cycle can be increased. In other words, if the main injection amount per cycle decreases with increasing cooling water temperature or the elapsed time after starting, as in the second aspect, the rising of cooling water temperature or the time after starting with the total air-fuel ratio kept lean. As the time elapses, it is possible to increase the number of sub-injection cylinders, thereby effectively realizing the oxidation of HC and CO and the increase of the exhaust temperature.
[0018]
According to the third aspect of the invention, the mixing of the air and the surplus fuel in the exhaust port and the exhaust passage is promoted more than the case where the sub-injections are not performed at equal intervals, and accordingly, the oxidation of HC and CO and the exhaust temperature increase. Is effective.
[0019]
According to the fourth aspect of the invention, the total air-fuel ratio under the conditions for performing the sub-injection can be made lean even if the injection characteristics of the means for performing the sub-injection vary or deteriorate with time.
[0020]
According to the fifth aspect of the present invention, even if the injection characteristic of the means for performing the sub-injection varies or deteriorates with time from the time of the first sub-injection at the time of the next start as long as it does not change from the cooling water temperature at the time of the current start, The total air-fuel ratio can be matched to the lean target value.
[0021]
Although the sub-injection is intended to raise the temperature of the catalyst at the time of low temperature start, if the combustion chamber, the exhaust port and the exhaust passage are not warmed to some extent, the surplus fuel from the sub-injection cannot be oxidized and the effect of increasing the exhaust temperature can be achieved. Although it may not be desired, according to the seventh invention, when the water temperature at start-up is less than a predetermined value and the time after start-up is less than a predetermined value, the condition that the sub-injection is not performed is set, that is, the combustion chamber, the exhaust port Further, since the sub-injection is not performed until the exhaust passage is warmed to some extent, wasteful fuel consumption can be suppressed.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a control system for an in-cylinder direct injection spark ignition engine.
[0023]
In the figure, 1 is an engine body, 2 is a combustion chamber, 3 is a piston, 4 is a spark plug, 5 is a fuel injection valve, 6 is an intake valve, 7 is an exhaust valve, 8 is a swirl control valve, 9 is a DC motor, etc. The throttle valve is driven by a throttle actuator. In-cylinder direct injection type spark ignition engines are provided with fuel injection valves facing the combustion chamber and devised shapes of the combustion chamber, intake port, and piston top surface. Since the invention is irrelevant, it is shown briefly in FIG.
[0024]
The ECU 11 receives signals from an air flow sensor 12 that detects the air flow rate upstream of the throttle valve 9, a crank angle sensor 13, and a sensor 14 that detects the engine coolant temperature, together with signals from the O ₂ sensor 15, etc. Based on this signal, the mixture is unevenly distributed only in the vicinity of the spark plug 4 at the time of engine low load and combustion (stratified combustion) is performed, so that the average air-fuel ratio in the combustion chamber is operated at an air-fuel ratio of 30 to 40, for example. When the engine is out of low load, a homogeneous air-fuel mixture is formed in the combustion chamber and the average air-fuel ratio in the combustion chamber is made richer than the low load (theoretical air-fuel ratio and output air-fuel ratio). Control.
[0025]
In the middle of the exhaust passage 21, catalytic converters 22 and 23 are provided on the upstream side and the downstream side. Of these, only the three-way catalyst is disposed in the upstream catalytic converter 22, and the three-way catalyst and the lean NOx catalyst are disposed in this order from the upstream side in the downstream catalytic converter 23. The original catalyst simultaneously oxidizes HC and CO in the exhaust gas and reduces NOx. Further, NOx generated in the stratified combustion zone is purified by the lean NOx catalyst.
[0026]
On the other hand, in order to quickly activate the catalyst in the catalytic converter installed in the exhaust passage 21 at the time of low temperature start, the ECU 11 performs the main injection in the intake stroke or the compression stroke and then continues in the expansion stroke or the exhaust stroke. A secondary injection is performed. The combustion of the sub-injection fuel discharged unburned into the exhaust passage 21 raises the temperature of the exhaust, or the sub-injection fuel reaches the catalyst and burns, thereby raising the temperature of the catalyst early. is there.
[0027]
Now, it is known that when the sub-injection is performed, it is desirable that the total air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and therefore, the sub-injection per cycle at the time of low temperature start when the main injection amount per cycle increases. Although the amount must be relatively small, the minimum injection amount SR exists as a characteristic of the fuel injection valve, and an injection amount below this cannot be set as a single sub-injection amount for one cylinder. If sub-injection is performed in all cylinders with one sub-injection amount per cylinder, the total air-fuel ratio may be richer than the stoichiometric air-fuel ratio.
[0028]
Therefore, the ECU 11 performs the sub-injection only in a limited number of cylinders at a low temperature start when the main injection amount per cycle is large and the sub-injection amount per cycle must be relatively small.
[0029]
This control executed by the ECU 11 will be described with reference to the flowchart of FIG. This routine is executed once every two engine revolutions (per cycle).
[0030]
First, in S1, the intake air flow rate Qa from the air flow meter and the cooling water temperature TW from the water temperature sensor are read, and a table having the contents shown in FIG. 3 in S2 is retrieved from the cooling water temperature TW to obtain the target per cycle of main injection. The air-fuel ratio A is obtained, and from this target air-fuel ratio A and the intake air flow rate Qa (assumed to be substantially equal to the intake air amount per cycle), in S3,
[Expression 1]
F1 = Qa / A
The main injection amount F1 per cycle is calculated by the following formula.
[0032]
The characteristics of the main injection amount F1 per cycle are the same as in the conventional case as shown in FIG. 3 (F1 increases as TW decreases). The characteristic shown in FIG. 3 is that the combustion by the main injection at the time of low-temperature start is slower than after the warm-up is completed, so it is necessary to enrich the air-fuel ratio compared to after the warm-up to ensure operability. Because there is.
[0033]
In S4, the engine starting water temperature TWINT is read, and the starting water temperature TWINT is compared with a predetermined value TWDAN in S5. If the starting water temperature is equal to or higher than the predetermined value, it is determined that the catalyst is in an active state, and the process proceeds from S5 to S6. After the sub-injection determination flag FLGTINJ = 0 (that is, sub-injection is unnecessary) In step S7, the main injection amount F1 per cycle is stored in a predetermined RAM, and the current process is terminated. The engine starting water temperature can be obtained by storing the cooling water temperature when the ignition key switch is turned on in a predetermined RAM.
[0034]
On the other hand, if TWINT <TWDAN, it is determined that the catalyst is in an inactive state, the process proceeds from S5 to S8, and the timer TIME is read. This timer TIME is activated when an ignition key switch is turned on in a flow (not shown), and measures time (elapsed time from the start).
[0035]
In step 9, the timer TIME is compared with the start time TIMST of the secondary injection and the end time TIMEND of the secondary injection (however, TIMEEND> TIMST). (1) When the timer TIME is less than or equal to the sub-injection start time TIMST, and (2) when the timer TIME is greater than or equal to the sub-injection end time TIMEEND, the processes of S6 and S7 are performed to prevent the sub-injection from being performed. To end the current process.
[0036]
Here, the reason why the sub-injection is not performed under the condition (1) is as follows. Although the sub-injection is intended to raise the temperature of the catalyst at the time of low temperature start, if the combustion chamber, the exhaust port and the exhaust passage are not warmed to some extent, the surplus fuel from the sub-injection cannot be oxidized and the effect of increasing the exhaust temperature can be achieved. There are things I can't expect. Therefore, the sub-injection is not performed until the combustion chamber, the exhaust port, and the exhaust passage are warmed to some extent (that is, when TIME ≦ TIMST).
[0037]
Further, the reason why the sub-injection is not performed under the condition (2) is that the role of the sub-injection ends after the catalyst is activated (that is, when TIME ≧ TIMEEND).
[0038]
The sub-injection start time TIMST and the sub-injection end time TIMEND are constant values, and may be allocated according to the starting water temperature TWINT as shown in FIGS.
[0039]
When the timer TIME exceeds the sub-injection start time TIMST and is less than the sub-injection end time TIMEEND, the process proceeds from S9 to S10, where the flag FLGTINJ = 1 (indicating that sub-injection is necessary).
[0040]
In subsequent S11, a target value of the total air-fuel ratio (hereinafter referred to as “target total air-fuel ratio”) B is obtained from the coolant temperature TW by referring to a table having the contents shown in FIG. As shown in FIG. 6, the target total air-fuel ratio B is determined to be leaner than the stoichiometric air-fuel ratio regardless of the coolant temperature.
[0041]
In S12, the target total air-fuel ratio B, the intake air flow rate Qa, and the target air-fuel ratio A that has already been obtained are used in S12.
[Expression 2]
F2 = Qa × (1 / B−1 / A)
The sub-injection amount F2 per cycle is calculated by the following formula.
[0043]
Here, Equation 2 is derived as follows. If the intake air amount per cycle is substantially equal to the intake air flow rate Qa, Qa / (F1 + F2) = B.
[Equation 3]
F2 = Qa / B-F1
The sub-injection amount F2 per cycle can be obtained from the equation (1). Equation (2) is obtained by eliminating F1 in combination with the equations (3) and (1). That is, the sub-injection amount F2 per cycle is calculated so that the total air-fuel ratio matches the target total air-fuel ratio B.
[0045]
In S13, a value obtained by dividing the sub-injection amount F2 per cycle by the minimum injection amount SR of the fuel injection valve and rounded down to the nearest decimal point (value converted to an integer) is calculated as the number N of cylinders performing sub-injection. After the number N of sub-injection cylinders and the sub-injection amount F2 per cycle are stored in a predetermined RAM in S14, the process of S7 is executed and the current process is terminated.
[0046]
Using the main injection amount F1 per cycle stored, the sub-injection amount F2 per cycle, and the number N of sub-injection cylinders stored in this way, the main injection in one cycle is performed as follows by a routine not shown. And the secondary injection is executed. Hereinafter, a case of a four-cylinder engine will be described.
[0047]
<1> Main Injection: Since the main injection amount F1 per cycle is the total amount for four cylinders, the main injection amount per one cylinder is 1/4 of F1. This is converted into a fuel injection pulse width Ti and output for each cylinder. When the predetermined injection timing is reached, the fuel injection valve is opened for the time Ti.
[0048]
<2> Sub-injection: Sub-injection can be executed from the first ignition cylinder or the next ignition cylinder after the flag FLGTINJ = 1. One sub-injection amount per cylinder is calculated from the number N of sub-injection cylinders, and the sub-injection in which the calculated sub-injection amount is distributed at equal intervals in one cycle is executed.
[0049]
(1) When the number of sub-injection cylinders N = 1: The sub-injection amount F2 per cycle is directly used as one sub-injection amount for one cylinder. Sub-injection is executed in only one of the four cylinders. In this case, the cylinder that performs the sub-injection may be any of the four cylinders. For example, in the upper part of FIG. 7, the sub-injection cylinder is the # 1 cylinder.
[0050]
(2) When the number of sub-injection cylinders N = 2: One sub-injection amount of one cylinder is F2 / 2, and sub-injection is executed in two of the four cylinders. In this case, every other cylinder that performs sub-injection is in the ignition order. For example, in the middle stage of FIG. 7, the cylinders that perform the sub-injection are the # 1 cylinder and the # 4 cylinder. At this time, the gas when only the main injection is performed and the sub-injection is performed and the gas that has become richer is alternately and continuously discharged into the exhaust passage, and the unburned gas and air are mixed. It becomes easy and exothermic reaction improves. On the other hand, if the cylinders that perform the sub-injection are continuous cylinders such as the # 1 cylinder and the # 3 cylinder, the unburned gas and the air are not easily mixed, and the exothermic reaction is worsened.
[0051]
(3) When the number of sub-injection cylinders N = 3: One sub-injection amount of one cylinder is F2 / 3, and sub-injection is executed in three of the four cylinders. When selecting 3 cylinders out of 4 cylinders, there is no such standard as when selecting 2 cylinders out of 4 cylinders. For example, in the lower part of FIG. 7, the cylinders that perform the sub-injection are three cylinders (# 1, # 3, and # 4) in which the ignition order is continuous.
[0052]
{Circle around (4)} When the number of sub-injection cylinders N = 4, sub-injection is executed for each cylinder with the amount of one sub-injection per cylinder as F2 / 4.
[0053]
(5) When the number of sub-injection cylinders is switched: For example, when sub-injection is performed in only two of the four cylinders, it is shifted to sub-injection of only one of the four cylinders due to an increase in the coolant temperature. There is. In this case, it is necessary to prevent the sub-injection cylinders from continuing at the connecting portion.
[0054]
If the value of one sub-injection amount per cylinder (F2 / 2 for (2), F2 / 3 for (3), F2 / 4 for (4)) has a value below the decimal point, It may be converted into an integer by rounding down.
[0055]
Thus, in the present embodiment, the sub-injection amount F2 per cycle is calculated so that the total air-fuel ratio becomes the lean target value, and the sub-injection amount of one cylinder is calculated from the sub-injection amount F2 per cycle. The number of sub-injection cylinders N is calculated so that the fuel injection amount is equal to or greater than the minimum injection amount, and the sub-injection is performed with only a limited number of cylinders in one cycle. The fuel ratio can be made lean (see FIG. 8). In addition, since the sub-injection cylinders are distributed at regular intervals during one cycle, mixing of air and surplus fuel in the exhaust port and exhaust passage is promoted, thereby oxidizing the HC and CO and increasing the exhaust temperature. Can be realized effectively.
[0056]
The flowchart of FIG. 9 is a second embodiment, which replaces FIG. 2 of the first embodiment. The same step numbers are assigned to the same parts as in FIG.
[0057]
Now, the actual total air-fuel ratio may deviate from the target total air-fuel ratio B and be biased to the rich side or lean side due to variations in the flow characteristics of the fuel injection valve 5 and the air flow meter 12 and deterioration over time. Therefore, in the second embodiment, even if there are variations or deterioration with time in the flow characteristics of the fuel injection valve 5 and the air flow meter 12, the actual total air-fuel ratio matches the target total air-fuel ratio B per cycle. The sub-injection amount F2 is corrected.
[0058]
The difference from FIG. 2 will be mainly described. In S21, K (= C / B) which is the ratio of the actual total air-fuel ratio C and the target total air-fuel ratio B (set to the initial value of 1.0 at the start) is set. Read and use this ratio K in S22 [0059]
[Expression 4]
F2H = F2 × K
The sub-injection amount F2 per cycle is corrected (the corrected value is referred to as a corrected sub-injection amount F2H per cycle), and the sub-injection cylinder is changed from this corrected sub-injection amount F2H per cycle to S23. The number N2 is calculated (the value obtained by dividing F2H by the minimum injection amount SR is rounded down to the sub-injection cylinder number N2).
[0060]
In S24 and S25, the exhaust air-fuel ratio under the condition of performing the sub-injection is read as the actual total air-fuel ratio C, the ratio of this actual total air-fuel ratio C to the target total air-fuel ratio B is calculated and put into K. The number of sub-injection cylinders N2 and the corrected sub-injection amount F2H per cycle are stored in a predetermined RAM in S26.
[0061]
A sensor for detecting the exhaust air-fuel ratio includes a wide-area air-fuel ratio sensor. For example, this wide-area air-fuel ratio sensor is attached upstream of the catalyst.
[0062]
According to the second embodiment, when the actual total air-fuel ratio C is biased to the rich side with respect to the target total air-fuel ratio B due to variations in flow characteristics of the fuel injection valve and the air flow meter, the ratio K is 1.0. As a result, the sub-injection amount F2 per cycle is corrected to decrease by the value K smaller than 1.0, so that the actual total air-fuel ratio becomes the lean side, that is, the target total air-fuel ratio B. Returned. Conversely, when the actual total air-fuel ratio C is leaner than the target total air-fuel ratio B, K is stored as a value larger than 1.0, and F2 is caused by K larger than 1.0. Thus, the actual total air-fuel ratio is returned to the rich side, that is, the target total air-fuel ratio B.
[0063]
Thus, according to the second embodiment, the sub-injection amount F2 per cycle is corrected so that the actual total air-fuel ratio matches the target total air-fuel ratio B. Therefore, the fuel injection valve 5 and the air flow meter 12 are corrected. Even if there are variations in the flow characteristics and deterioration with time, the total air-fuel ratio when the cooling water temperature at the start is low can be made leaner than the stoichiometric air-fuel ratio.
[0064]
In the second embodiment, the correction of the sub-injection amount F2 per cycle is started from K = 1.0 each time the engine is started, that is, the correction is performed again every time the engine is started. The actual total air-fuel ratio C may always deviate from the target total air-fuel ratio B before the correction of the sub-injection amount F2 per cycle (that is, at the time of the first sub-injection).
[0065]
To cope with this, the ratio K is configured as a learning value assigned to the cooling water temperature. By using K as a learning value and backing up even after the ignition key switch is turned off, the fuel injection valve 5 and the air flow meter will be used from the first sub-injection at the next start if the cooling water temperature at the current start does not change at the next start. The actual total air-fuel ratio C can be made to coincide with the target total air-fuel ratio B even if there is a variation in each of the 12 flow characteristics.
[0066]
In the embodiment, the sub-injection is performed when the timer TIME satisfies the condition of TIMST <TIME <TIMEEND (S8, S9). However, when the coolant temperature TW satisfies the condition of TWST <TW <TWEND, the sub-injection is performed. You can do it. In this case, the lower limit value TWST and the upper limit value TWEND can be changed according to the starting water temperature TWINT in the same manner as in FIGS.
[0067]
Not only the cooling water temperature but also a representative value of engine temperature (for example, oil temperature) may be used.
[0068]
The number and arrangement of the catalytic converters are not limited to those shown in FIG.
[0069]
In the embodiment, the case where the sub-injection amount F2 per cycle is calculated using a mathematical formula has been described. However, as in the case of the main injection amount per cycle, a table assigned to the coolant temperature is searched for per cycle. It is also possible to obtain the secondary injection F2.
[0070]
In the embodiment, the case of four cylinders has been described, but the present invention is not limited to this case.
[Brief description of the drawings]
FIG. 1 is a control system diagram of a first embodiment.
FIG. 2 is a flowchart for explaining calculation of a main injection amount F1 and a sub injection amount F2 per cycle, and a sub injection cylinder number N;
FIG. 3 is a characteristic diagram of a target air-fuel ratio A for main injection and a main injection amount F1 per cycle with respect to the coolant temperature.
FIG. 4 is a characteristic diagram of sub-injection start time with respect to water temperature at start-up.
FIG. 5 is a characteristic diagram of the sub-injection end time with respect to the water temperature at start.
FIG. 6 is a characteristic diagram of a target total air-fuel ratio B with respect to cooling water temperature.
FIG. 7 is a diagram for explaining an arrangement of cylinders that perform sub-injection.
FIG. 8 is a characteristic diagram for explaining the operation of the present invention.
FIG. 9 is a flowchart for explaining calculation of a main injection amount F1 and a corrected sub injection amount F2H per cycle and a sub injection cylinder number N2 in the second embodiment.
FIG. 10 is a flow characteristic diagram of a fuel injection valve.
FIG. 11 is a characteristic diagram for explaining the operation of the conventional device.
FIG. 12 is a view corresponding to claims of the first invention.
[Explanation of symbols]
5 Fuel Injection Valve 14 Water Temperature Sensor 22, 23 Catalytic Converter

Claims (7)

In the in-cylinder direct injection spark ignition engine in which the main injection is performed in the intake stroke or the compression stroke at the time of cold start, and then the sub-injection is performed in the expansion stroke or the exhaust stroke.
Means for calculating the sub-injection amount per cycle so that the total air-fuel ratio becomes a lean target value at the time of low temperature start;
Means for calculating the number of sub-injection cylinders from the sub-injection amount per cycle and the minimum injection amount of the fuel injection valve characteristic;
Means for selecting a cylinder that performs sub-injection from the calculated number of sub-injection cylinders;
An in-cylinder direct injection spark ignition engine characterized by comprising means for performing sub-injection only with the selected cylinder under conditions for performing sub-injection. The in-cylinder direct injection spark ignition engine according to claim 1, wherein the number of sub-injection cylinders is increased with an increase in cooling water temperature or a lapse of time after starting. The in-cylinder direct injection spark ignition engine according to claim 1 or 2, wherein a cylinder that performs sub-injection is selected so that sub-injection is performed at equal intervals in one cycle section. The in-cylinder direct injection system according to any one of claims 1 to 3, wherein the sub-injection amount per cycle is corrected so that an actual total air-fuel ratio matches a lean target value. Spark ignition engine. The difference between the actual total air-fuel ratio and the lean target value is stored as a learned value, and the sub-injection amount per cycle at the next start is corrected with the stored learned value. The in-cylinder direct injection spark ignition engine according to any one of 3 to 3. The condition for performing the sub-injection is determined from a parameter representing a low temperature state at the time of starting or a parameter representing an intermediate state of engine warm-up after the starting. In-cylinder direct injection spark ignition engine. The in-cylinder direct injection spark ignition engine according to claim 6, wherein the sub-injection is not performed when the starting water temperature is less than a predetermined value and the time after starting is less than a predetermined value.

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