JP2003013785A - Control device for direct injection spark ignition type internal combustion engine - Google Patents

Abstract

(57) [Problem] To effectively utilize knock improvement control for suppressing stratification of an air-fuel mixture to suppress occurrence of knock. In a predetermined operation range, a part of required fuel is injected by an intake fuel injection valve during an exhaust stroke to form a lean mixture in the entire combustion chamber, and the remaining fuel is supplied to a cylinder. When the engine speed exceeds a predetermined speed in an internal combustion engine that performs knock improvement control that suppresses the generation of knock by sub-stratifying the air-fuel mixture by injecting during the compression stroke by the internal direct fuel injection valve 12 , The knock improvement control is prohibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a direct injection spark ignition type internal combustion engine which suppresses knocking by substratifying an air-fuel mixture in a predetermined operation region.

[0002]

2. Description of the Related Art Conventionally, a part of fuel is injected during an intake stroke to form a homogeneous mixture in a combustion chamber, and the remaining fuel is injected during a compression stroke to form a stratified mixture around a spark plug. There is known a spark ignition type internal combustion engine (see Japanese Patent Laid-Open No. 5-118244).

[0003]

By the way, in a high load region where knock is likely to occur, the fuel is divided into the intake stroke and the compression stroke and injected as described above, so that the occurrence of knock can be suppressed. That is, the amount of fuel that makes the entire combustion chamber lean is injected in the intake stroke, and the remaining fuel is injected in the compression stroke to form a sub-stratified mixture in the combustion chamber, thereby leaning the end gas portion and knocking. It suppresses and improves the occurrence of.

As a result of performing such knock improvement control,
In the low rotation speed region, as shown in FIG. 6 (A), when knock improvement control is performed (solid line), compared with normal control (broken line) in which all required fuel is directly injected into the cylinder during the intake stroke. ) Can increase the generated torque (a torque improving effect can be obtained). This is because the knock characteristic is poor, and the ignition timing is set to MBT (Ignition timing at which maximum torque is obtained: Minimum advance for).
In the low rotation speed region in which it is unavoidable to set the time away from the Best Torque), it becomes possible to advance the ignition timing by the knock improvement control.
The engine generated torque becomes large.

However, when the knock improvement control is performed in the high rotation speed region, as shown in FIG. 6 (B), the knock improvement control (solid line) is more than the normal control (broken line). There is a problem that the engine generated torque becomes small. This is because the knock characteristic in the high rotation range is better than that in the low rotation range, and the ignition timing is not so far from the MBT. Therefore, rather than the torque improving effect by advancing the ignition timing by the knock improving control, By injecting a part of this during the compression stroke (after the intake valve is closed), the effect of improving the intake density by effectively utilizing the latent heat of vaporization, which is the characteristic of in-cylinder direct injection, is diminished, and the intake air amount is reduced. It is thought that the effect of the loss is greater.

The present invention has been made in order to solve the conventional problems as described above, and in a high load region where the occurrence of knocking is a problem, it is possible to effectively secure the generated torque while effectively knocking. It is an object of the present invention to provide a control device for a direct injection spark ignition type internal combustion engine that can be avoided.

[0007]

Therefore, the invention according to claim 1 is a control device for a direct injection spark ignition type internal combustion engine, which performs a substratified combustion by forming a substratified mixture in a predetermined operating region. In the high rotation speed region where the engine rotation speed exceeds the predetermined rotation speed, the sub-stratified combustion is prohibited, and in the high rotation speed region where the rotation speed of the engine exceeds the predetermined rotation speed, the engine generated torque during the sub-stratification combustion sucks all the required fuel. It is characterized in that it becomes smaller than the engine generated torque when the fuel is injected into the cylinder during the stroke.

The invention according to claim 2 is provided with an intake portion fuel injection valve for injecting fuel into the intake passage in front of the combustion chamber, and a part of the required fuel is exhausted by the intake portion fuel injection valve. It is characterized by performing a sub-stratified combustion by injecting into the inside of the cylinder to form a lean mixture and injecting the remaining fuel directly into the cylinder during the compression stroke.

According to the third aspect of the invention, during the intake stroke, a portion of the required fuel is directly injected into the cylinder to form a lean mixture in the entire combustion chamber, and the remaining fuel is compressed during the compression stroke. It is characterized by performing sub-stratified combustion by directly injecting into the cylinder.

The invention according to claim 4 is characterized in that the predetermined rotation speed is set to a higher rotation speed side as the octane number of the fuel is higher.

[0011]

According to the first aspect of the present invention, the engine generated torque during the substratified operation is lower than the engine generated torque when all the required fuel is directly injected into the cylinder during the intake stroke. Since the sub-stratification operation is prohibited in the rotation speed range where it becomes like this, the knock improvement control can be effectively utilized, and the torque reduction due to the knock improvement control can be surely prevented. You can

Particularly, in the high load region, the knock improvement control is performed only in the low / middle rotation region where knock is likely to occur, so that advantageous effects of knock improvement control such as suppression of knock generation and torque improvement are achieved. Can be surely obtained. According to the second aspect of the present invention, a part of the required fuel is injected into the intake passage by the intake fuel injection valve during the exhaust stroke, and the remaining fuel is directly injected into the cylinder during the compression stroke. As a result, a lean air-fuel mixture can be reliably formed in the entire combustion chamber and substratification can be performed.

According to the third aspect of the present invention, in order to form a lean air-fuel mixture in the entire combustion chamber, knock improvement control is performed by one in-cylinder direct injection fuel injection valve without providing a separate fuel injection valve. Can be carried out, and the knock improvement effect can be surely utilized in such an organization. According to the invention of claim 4, the knock improving effect can be maximized for fuels having different octane numbers.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the system diagram shown in FIG. 1, a combustion chamber 1 of an engine is defined by a cylinder head 2, a cylinder block 3 and a piston 4, and an intake passage 5 and an exhaust passage 6 are connected to the combustion chamber 1. Has been done.

An intake valve 7 that is opened and closed by an intake cam (not shown) is provided at the open end of the intake passage 5 on the combustion chamber 1 side, and an exhaust valve (not shown) at the open end of the exhaust passage 6 on the combustion chamber 1 side is provided. An exhaust valve 8 that is opened and closed by a cam is provided. The intake passage 5 is provided with an air flow meter 9 for detecting the intake air amount Qa, a throttle valve 10 for controlling the intake air amount Qa, and an intake fuel injection valve 11.
The intake fuel injection valve 11 injects fuel into the intake passage 5 in front of the combustion chamber 1.

Below the intake passage 5 of the cylinder head 2,
An in-cylinder direct injection fuel injection valve 12 for injecting fuel is provided in the combustion chamber 1, and the ignition plug 13 is arranged so as to face a substantially central portion of the combustion chamber 1. The intake portion fuel injection valve 11
The in-cylinder direct injection fuel injection valve 12 is opened by a drive signal from the engine control unit (ECU) 14,
The valve opening time is controlled to inject a predetermined amount of fuel.

When fuel is injected by the intake fuel injection valve 11 during the exhaust stroke, the injected fuel diffuses into the combustion chamber 1 to form a homogeneous mixture. When fuel is injected by the in-cylinder direct injection fuel injection valve 12 during the compression stroke, a concentrated air-fuel mixture is formed in the vicinity of the spark plug 13. Therefore, a part of the required fuel is injected by the intake fuel injection valve 11 during the exhaust stroke, and the remaining fuel is injected by the in-cylinder direct injection fuel injection valve 12 during the compression stroke, whereby the substratified combustion is performed. It can be performed.

On the other hand, the in-cylinder direct injection fuel injection valve 12 injects and ignites all of the required fuel during the intake stroke for homogeneous combustion, and the injection and ignition during the compression stroke for stratification. It is also possible to carry out combustion. Exhaust gas of the engine is discharged from the combustion chamber 1 to the exhaust passage 6 via the exhaust valve 8 and is discharged into the atmosphere via an exhaust purification catalyst (not shown).

The ECU 14 detects an air flow meter 9 for detecting the intake air amount Qa, a crank angle sensor 15 for detecting the rotational angle position of the crankshaft, a water temperature sensor 16 for detecting the engine cooling water temperature Tw, and an accelerator opening degree ACC. Signals from the accelerator opening sensor 17, an air-fuel ratio sensor (not shown), etc. are input. The engine speed N
e is calculated based on the signal from the crank angle sensor 15.

Then, the ECU 14 performs predetermined arithmetic processing based on these input signals to control the throttle opening of the throttle valve 10, the intake portion fuel injection valve 11 and the in-cylinder direct injection fuel injection valve 12. The fuel injection amount and injection timing control, the ignition timing control by the spark plug 13 and the like are performed.
As a combustion method of this engine, in the low and medium load regions where knock does not occur, in combination with air-fuel ratio control, stratified lean combustion (target air-fuel ratio tA /
F is about 40), homogeneous lean combustion (target air-fuel ratio tA / F)
Is about 20 to 30), there is homogeneous stoichiometric combustion, and either combustion method (and target air-fuel ratio tA / F) can be set according to engine operating conditions (engine rotation speed Ne, target engine torque tT).

In a high load region where knock may occur, the required fuel is divided and the fuel is injected, and the air-fuel mixture in the combustion chamber 1 is sub-stratified to suppress the knock. The improvement control is performed, but when the engine rotation speed exceeds a predetermined rotation speed, the knock improvement control is prohibited (that is, the knock improvement control is performed only in the high load / low / medium rotation range).

Specifically, part of the fuel is injected by the intake fuel injection valve 11 during the exhaust stroke (hereinafter referred to as exhaust stroke injection) to form a lean mixture in the entire combustion chamber 1. By injecting the remaining fuel by the in-cylinder direct injection fuel injection valve 12 during the compression stroke (hereinafter referred to as compression stroke injection) to form a sub-stratified mixture in the combustion chamber 1, the end gas portion becomes lean. Suppresses the occurrence of knock.

The fuel injection amount in the knock improvement control (that is, the required fuel amount tQf) is the total fuel amount of the fuel by the exhaust stroke injection and the fuel by the compression stroke injection. Fuel ratio or a slightly rich air-fuel mixture (for example, the target air-fuel ratio tA / F is 12 to 1
4.7) is set. The knock improvement control according to the present embodiment will be described below.

FIG. 2 is a flowchart showing knock improvement control. In step 1 (denoted as S1 in the figure; the same applies hereinafter), the intake air amount Qa, the engine rotation speed Ne, and the target engine torque tT are read. In step 2, it is determined whether or not the current engine operating condition is in a load (that is, a high load region) for performing knock improvement control.

If the engine operating condition is in the high load region, the routine proceeds to step 3. If it is not in the high load region, this control is terminated and normal control of stratified combustion or homogeneous combustion is performed according to the operating condition. In step 3, the engine speed Ne
Performs a knock improvement control to determine whether the rotation speed is equal to or lower than a predetermined rotation speed Ns that can also obtain the torque improvement effect.

The engine rotation speed Ne is the predetermined rotation speed N.
If s or less, the process proceeds to step 4 and the predetermined rotation speed N
If it exceeds s, this control is terminated, and normal control that is stratified combustion or homogeneous combustion is performed according to operating conditions. The torque improving effect referred to here means the knock improving control rather than the engine generated torque when all the required fuel is directly injected into the cylinder during the intake stroke under the same engine rotation speed. It means that the torque generated by the engine becomes larger when it is performed.

As described above, since the knock limit ignition timing can be advanced by performing the knock improvement control, it is possible to advance the ignition timing and increase the engine generated torque. However, the engine speed Ne
Exceeds a predetermined rotation speed Ns, a portion of the fuel is injected during the compression stroke rather than the increase in the torque due to the advance of the ignition timing, so that the effective use of the latent heat of vaporization, which is the characteristic of the direct cylinder injection, is performed. However, there is a problem that the torque reduction (reduction in intake air amount) due to the decrease in the torque becomes larger.

Further, in the high rotation region, there is less fear of knocking as compared with the middle / low rotation region. Therefore, the knock improvement control is performed only when the engine rotation speed Ne is equal to or lower than the predetermined rotation speed Ns, and the knock improvement control is prohibited when the engine rotation speed Ne exceeds the predetermined rotation speed Ns. Here, the predetermined rotation speed Ns is set to a value obtained in advance by experiments or the like, but a different value may be set depending on the octane number of the fuel. in this case,
For example, the rotation speed is set higher when regular gasoline is used than when high-octane gasoline is used.

In step 4, the required fuel injection amount tQf is calculated based on the target air-fuel ratio tA / F and the intake air amount Qa, for example, by referring to a preset map. As described above, the split fuel injection (as a whole)
The output air-fuel ratio tA / F is preset to the stoichiometric air-fuel ratio or slightly rich (A / F is 12 to 14.3), and the required fuel injection amount tQf is the fuel amount injected in the exhaust stroke injection (exhaust stroke injected fuel Amount Qe and the amount of fuel injected in the compression stroke injection (compression stroke injected fuel quantity) Qp.

In step 5, the exhaust stroke injection fuel amount Qe
And the compression stroke injection fuel quantity Qp are shown in the table (engine rotation speed Ne-intake injection fuel quantity ratio KPAR
Set it by referring to T). The optimum fuel ratio varies depending on the specifications and the like, and is a value that changes depending on the piston shape or the strength of gas flow. In the present embodiment, when the engine rotation speed Ne is 1000 rpm, the ratio of the exhaust stroke injection fuel amount Qe and the stroke stroke injection fuel amount Qp is about 5: 5,
When the engine speed Ne is 2000 rpm, the ratio of Qe and Qp is about 4: 6, and the engine speed Ne is 30.
At 00 rpm, the ratio of Qe and Qp is about 3: 7.

In step 6, the exhaust stroke injection end timing is set, and in step 7, the intake stroke injection is executed at a predetermined timing. For example, as shown in FIG. 5A, the injection end timing (that is, the valve closing timing) is 30 ° to 50 ° B.
The intake-portion fuel injection valve 11 is controlled so as to reach TDC (the crank angle position of 30 ° to 50 ° before exhaust top dead center), and the exhaust stroke injection fuel amount Qe set in step 5 is injected.

Incidentally, the reason why the exhaust stroke injection is controlled as the injection end timing in this way is to surely and sufficiently vaporize the fuel to form a homogeneous and lean air-fuel mixture in the cylinder. In step 8, the compression stroke injection start timing is set with reference to the table (engine speed Ne-injection start timing ITCOMP) as shown in FIG.

Although the optimum injection start timing varies depending on the specifications and the like, in this embodiment, the injection start timing ITCOMP
2 when the engine speed Ne is 1000 rpm
About 60 ° ATDC (crank angle position of 260 ° after compression top dead center), about 220 ° ATDC when the engine speed Ne is 2000 rpm, and the engine speed Ne is 3
At 000 rpm, it is set to about 200 ° ATDC.

In step 9, compression stroke injection is executed. That is, as shown in FIG. 5 (A), the in-cylinder direct injection fuel injection valve 12 is controlled so that the injection start timing (that is, the valve opening timing) becomes the injection start timing ITCOMP set in step 8. The compression stroke injection fuel amount Qp set in step 5 is injected. The reason why the compression stroke injection is controlled as the injection start timing is that the determination of the injection timing can be delayed as much as possible during the transition, and the knock improvement control can be effectively performed.

As described above, when the fuel is split and injected in the exhaust stroke and the compression stroke, and the air-fuel mixture is substratified to perform knock improvement control, the engine speed Ne is also improved by the knock improvement control. It is determined whether or not the rotation speed is lower than the predetermined rotation speed Ns and is executed only when the rotation speed is equal to or lower than the predetermined rotation speed Ns. When the rotation speed exceeds the predetermined rotation speed Ns, it is prohibited. It surely prevents torque reduction in the rotation range and
In the middle rotation range, knock and torque can be effectively improved.

In the above description, the intake portion fuel injection valve 11 is provided separately from the in-cylinder direct injection fuel injection valve 12 to perform the exhaust stroke injection. However, the present invention is not limited to this. The present invention may be applied to an engine of a type in which the intake stroke injection and the compression stroke injection are performed only by the injection valve 12. In this case, as shown in FIG. 5B, the injection start timing control is performed for both the intake stroke injection and the compression stroke injection. For example, the in-cylinder direct injection fuel injection valve 12 is controlled so that the intake stroke injection start timing is about 20 to 50 ° ATDC. The flowchart at this time is shown in FIG. Steps in the figure that are the same as those in the flowchart in FIG. 2 are given the same numbers as in FIG. In FIG. 7, in step 5 ′, the intake stroke injection fuel amount Qi is calculated, and in step 6 ′, the intake stroke injection start timing is set.

In step 7 ', the intake stroke injection fuel amount Qi calculated in step 5'is injected, and the compression stroke injection is performed in the same manner as in steps 8 and 9 in FIG. Further, almost no fuel exists in the end gas portion by stratifying the air-fuel mixture by injecting all of the requested fuel directly into the cylinder during the compression stroke without performing the intake stroke injection as in the above embodiment. Since it does not occur, knocking can be suppressed. Even in an internal combustion engine of a type in which the air-fuel mixture is stratified to perform knock improvement control, the engine rotation speed is equal to or lower than a predetermined rotation speed. By prohibiting knock improvement control (stratification of the air-fuel mixture), knock improvement control can be effectively utilized as in the case of the above embodiment.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing knock improvement control according to an embodiment.

FIG. 3 is a diagram showing an example of a table for calculating a fuel ratio to be injected in an intake stroke during substratified operation.

FIG. 4 is a diagram showing an example of a table for calculating injection start timing of compression stroke injection during substratified operation.

FIG. 5 is a timing chart showing fuel injection timing during substratified operation (A: when an intake portion fuel injection valve and an in-cylinder direct injection fuel injection valve are used together, B: only an in-cylinder direct injection fuel injection valve is used. If).

FIG. 6 is a diagram showing a relationship between ignition timing and engine generated torque (A: low rotation range, B: high rotation range).

FIG. 7 is a flowchart showing knock improvement control according to another embodiment.

[Explanation of symbols]

1 combustion chamber 2 cylinder head 3 cylinder block 11 Intake fuel injection valve 12 In-cylinder direct injection fuel injection valve 13 Spark plug 14 Engine control unit (ECU) 15 Crank angle sensor 16 Water temperature sensor 17 Accelerator position sensor

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 41/02 F02D 41/02 330F

Claims (4)

[Claims] 1. A controller for a direct injection spark ignition type internal combustion engine which forms a sub-stratified air-fuel mixture and performs sub-stratified combustion in a predetermined operating region, in a high rotation region where the rotational speed of the engine exceeds a predetermined rotational speed. In sub-stratified combustion is prohibited in the above, the engine generated torque during sub-stratified combustion is higher than the engine generated torque when injecting all of the required fuel into the cylinder during the intake stroke in the high rotation speed range exceeding the predetermined rotation speed. A control device for a direct injection spark ignition type internal combustion engine, characterized in that 2. An intake-portion fuel injection valve for injecting fuel into an intake passage in front of a combustion chamber, wherein the intake-portion fuel injection valve injects a portion of required fuel during an exhaust stroke to burn the fuel. The control of a direct injection spark ignition type internal combustion engine according to claim 1, wherein a lean air-fuel mixture is formed in the entire chamber and the remaining fuel is directly injected into the cylinder during the compression stroke to perform substratified combustion. apparatus. 3. A part of required fuel is directly injected into the cylinder during the intake stroke to form a lean mixture in the entire combustion chamber, and the remaining fuel is directly injected into the cylinder during the compression stroke. The control device for a direct injection spark ignition type internal combustion engine according to claim 1, wherein the sub-stratified combustion is performed. 4. The direct injection spark ignition according to any one of claims 1 to 3, wherein the predetermined rotation speed is set to a higher rotation speed side as the octane number of the fuel is higher. Control device for internal combustion engine.