JPH1061463A - Fuel injection control device of direct injection spark ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a state of being impossible of injection due to a shortage of a charge time in a fuel injection valve in switching a compression stroke injection for a stratified charge combustion to an intake stroke injection for a uniform charge combustion in a direct injection spark ignition engine. SOLUTION: At the time of switching a compression stroke injection to an intake stroke injection, an injection timing of a first cylinder (#1 cylinder) of the intake stroke injection is corrected to be in an advancing side since the injection of the first cylinder (#1 cylinder) of the intake stroke injection is faster than that of a final cylinder (#2 cylinder) of the compression stroke injection. Accordingly, an injection timing difference is made equal to or greater than a predetermined value α corresponding to a request charge time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for a direct injection spark ignition type engine having an electromagnetically driven fuel injection valve (injector) for directly injecting fuel into a combustion chamber for each cylinder.

[0002]

2. Description of the Related Art Conventionally, in a direct-injection spark ignition engine, the combustion system is switched according to the operating condition of the engine (for example, engine speed and accelerator opening), specifically, homogeneous combustion and stratified combustion. It is considered that the switching is selectively performed in the following manner. In the case of homogeneous combustion, while controlling the air-fuel ratio to the stoichiometric air-fuel ratio (stoichiometric; A / F = 14.6), in order to secure the homogenization time of the air-fuel mixture, early timing, ie, the intake stroke of each cylinder (more specifically, The fuel is injected at a relatively early stage.

In the case of stratified charge combustion, the air-fuel ratio is set to lean (A /
F = 30 to 40), while injecting fuel at a late timing, that is, at the compression stroke (more specifically, at the middle stage of the compression stroke before ignition) to concentrate the fuel around the spark plug near the ignition timing. As described above, in the direct injection spark ignition engine, it is necessary to switch between the intake stroke injection and the compression stroke injection according to the operating state of the engine.

[0004]

FIGS. 5 and 6 show a four-cylinder engine (ignition order is # 1 → # 3 → # 4 →
5 shows the case of switching from the intake stroke injection to the compression stroke injection, and FIG. 6 shows the case of switching from the compression stroke injection to the intake stroke injection. Both are # 1
This is an example of switching from a cylinder.

Here, when switching from the intake stroke injection to the compression stroke injection as shown in FIG. 5, the injection of the first cylinder (# 1 cylinder) of the compression stroke injection is only delayed from the intake stroke to the compression stroke. No problem. However, when switching from the compression stroke injection to the intake stroke injection as shown in FIG. 6, it is necessary to advance the injection of the first cylinder (# 1 cylinder) of the intake stroke injection from the compression stroke to the intake stroke. It is not only necessary to perform the injection of the first cylinder (# 1 cylinder) of the intake stroke injection prior to the injection of the cylinder (# 2 cylinder), but also the difference ΔT between these injection timings becomes extremely short.

On the other hand, the drive of the direct injection type fuel injection valve requires a higher voltage than the type in which the fuel is injected into the intake system.
It is necessary to secure sufficient charging time. Therefore, when switching from the compression stroke injection to the intake stroke injection, in the example of FIG. 6, the injection of the first cylinder (# 1 cylinder) of the intake stroke injection and the injection of the last cylinder (# 2 cylinder) of the compression stroke injection are performed. Is extremely short, the charging time is insufficient, and the injection of the last cylinder (# 2 cylinder) of the compression stroke injection cannot be performed, which may cause a misfire, resulting in a deterioration in drivability and emission due to the misfire. There was a problem of doing.

The present invention has been made in view of the above-mentioned conventional problems, and when switching from compression stroke injection to intake stroke injection in a direct injection spark ignition type engine, it is possible to smoothly switch without causing misfiring or the like. The purpose is to.

[0008]

For this reason, in the invention according to claim 1, as shown in FIG. 1, an electromagnetically driven fuel injection valve for directly injecting fuel into a combustion chamber is provided for each cylinder. Switching means for switching the fuel injection timing to each cylinder to either the intake stroke or the compression stroke in accordance with the operation state of the engine, and each fuel injection valve in each cylinder in the intake stroke by an intake stroke injection command from the switching means. Intake stroke injection means for driving and performing fuel injection, and compression stroke fuel injection means for performing fuel injection by driving each fuel injection valve in the compression stroke of each cylinder by a compression stroke injection command from the switching means. In the fuel injection control device for a direct-injection spark ignition type engine, when switching from compression stroke injection to intake stroke injection is performed by the switching means, As the difference between the injection timing of the cylinder to be injected at the end by morphism timing and the compression stroke injection means is increased, characterized in that a switching injection timing correcting means for correcting at least one of injection timing.

As described above, when switching from the compression stroke injection to the intake stroke injection, at least one of the injection timing of the first cylinder of the intake stroke injection and the injection timing of the last cylinder of the compression stroke injection is corrected. By increasing the difference between these injection timings, it is possible to secure the charging time of the fuel injection valve and prevent the injection from becoming impossible.

In the invention according to claim 2, when switching from the compression stroke injection to the intake stroke injection is performed by the switching means,
The injection timing of the first cylinder injected by the intake stroke injection means is earlier than the injection timing of the last cylinder injected by the compression stroke injection means. It is characterized in that the injection timing of the first cylinder to be injected is corrected to the leading side by the means.

When the difference between the injection timings is increased, it is possible to correct the injection timing of the last cylinder of the compression stroke injection to a delay side. However, on the compression stroke side, HC, NOx, and smoke with respect to the change of the injection timing are changed. Because changes are sensitive, adverse effects are likely to occur. In this regard, it is preferable to correct the injection timing of the first cylinder in the intake stroke injection to the leading side, since the influence on HC, NOx, and smoke is small even if the injection timing is shifted on the intake stroke side. .

According to a third aspect of the present invention, the switching-time injection timing correction means includes a correction amount setting means for setting a correction amount such that a difference between the injection timings becomes a predetermined value. Thereby, the difference in the injection timing can be reliably ensured. The invention according to claim 4 is characterized in that the predetermined value is determined by a required charging time of the fuel injection valve.

Thus, the required charging time can be secured without excess or shortage.

[0014]

Embodiments of the present invention will be described below. FIG. 2 is a system diagram of a direct injection spark ignition type engine showing one embodiment of the present invention. The engine 1 is a four-cylinder engine in this example, and the ignition order is # 1 → # 3 → # 4 →
# 2.

On the cylinder head side of the combustion chamber 2 of each cylinder of the engine 1, an ignition plug 3 is disposed at the center. The intake port 4 and the exhaust port 5 surround the ignition plug 3.
Are formed, and an intake valve 6 and an exhaust valve 7 are mounted on each of them. Further, a fuel injection valve (injector) 8 is provided so as to inject fuel directly into the combustion chamber 2, and the fuel is supplied by a high-pressure fuel pump 9 through a fuel gallery 10 common to all cylinders, and the pressure is regulated by a pressure regulator. It is adjusted by 11.

The fuel injection valve 8 is electromagnetically driven, is energized by a drive pulse signal output from the control unit 12 and opens, and the injection timing is controlled by the output timing of the drive pulse signal. The injection time is controlled by the width to control the injection amount. Signals from various sensors are input to the control unit 12 for controlling the fuel injection of the fuel injection valve 8.

The various sensors include a crank angle sensor 13, an air flow meter 14, an accelerator sensor 15, and the like. The crank angle sensor 13 detects the reference crank angle (720 ° / 4 = 1) in synchronization with the rotation of the camshaft of the engine 1.
80 °), a reference signal REF including a cylinder discrimination signal is output, and a unit signal POS is output for each unit crank angle.
Thus, the crank angle θ can be detected, and the engine speed Ne can be calculated.

The air flow meter 14 is, for example, a hot wire type,
It is arranged in the intake passage of the engine 1 and outputs a signal corresponding to the intake air flow rate Qa. The accelerator sensor 15 outputs a signal corresponding to the accelerator opening (accelerator pedal depression amount) Acc, for example, by a potentiometer type. Here, the control unit 12 performs arithmetic processing according to a predetermined program (such as the injection timing control flow in FIG. 3) by a built-in microcomputer while inputting signals from these sensors, and
Is performed.

FIG. 3 is a flowchart of the injection timing control, which is executed in synchronization with the engine rotation by the reference signal REF of the crank angle sensor 13 and the like. Step 1
In (indicated as S1 in the figure, the same applies hereinafter), cylinder discrimination is performed based on the reference signal REF of the crank angle sensor 13. Here, the intake stroke cylinder (cylinder entering the intake stroke) is #
It is determined as n cylinders. Therefore, the compression stroke cylinder (cylinder entering the compression stroke) is determined to be the # n-1 cylinder immediately preceding the #n cylinder in the ignition order.

In step 2, the engine speed Ne and the intake air flow rate Qa (or accelerator opening Acc) are read as the engine operating state, and the combustion method is determined based on these. That is, one of the homogeneous combustion in which the air-fuel ratio is controlled stoichiometrically and the stratified combustion in which the air-fuel ratio is controlled lean is selected. In step 3, based on the combustion method,
Determine the fuel injection stroke. In the case of homogeneous combustion, intake stroke injection is performed, and in the case of stratified combustion, compression stroke injection is performed.

In step 4, it is determined whether or not the switching from the compression stroke injection to the intake stroke injection is performed. If not, the process proceeds to step 5. In step 5, it is determined whether or not the switching from the intake stroke injection to the compression stroke injection is performed. If not, the process proceeds to step 6. In step 6, it is determined whether the intake stroke injection or the compression stroke injection is performed. If the intake stroke injection is performed, the process proceeds to steps 7 and 8.
Proceed to 10. [In the case of intake stroke injection] In step 7, the injection timing in the intake stroke injection is set. Here, the injection timing is set relatively early in the intake stroke, but is changed according to the engine operating state, that is, the engine speed Ne and the intake air flow rate Qa (or the accelerator opening Acc).

In step 8, a drive pulse signal having a pulse width corresponding to a separately determined fuel injection amount is output to the #n cylinder during the intake stroke at the injection timing set in step 7, and Inject (intake stroke injection). [In the case of compression stroke injection] In step 9, the injection timing in the compression stroke injection is set. Here, the injection timing is set in the middle stage of the compression stroke before ignition, but is changed according to the engine operating state, that is, the engine speed Ne and the intake air flow rate Qa (or the accelerator opening Acc).

In step 10, a drive pulse signal having a pulse width corresponding to a separately determined fuel injection amount is output to the # n-1 cylinder in the compression stroke at the injection timing set in step 9. Then, fuel injection is performed (compression stroke injection). [At the time of switching from compression stroke injection to intake stroke injection] At the time of switching from compression stroke injection to intake stroke injection, the process proceeds to steps 11 to 17 as determined in step 4.

In step 11, similarly to step 7, the injection timing in the intake stroke injection is set.
In step 12, similarly to step 9, the injection timing in the compression stroke injection is set. In step 13, a timing difference ΔT from the injection timing of the intake stroke injection to the injection timing of the compression stroke injection is calculated.
It is desirable that the timing difference ΔT be obtained by converting the crank angle from the engine speed at that time into time.

In step 14, the timing difference ΔT is compared with a predetermined value α corresponding to the required charging time to determine whether ΔT <α. When the result of the comparison is that ΔT <α, the routine proceeds to step 15. In step 15, the injection timing of the intake stroke injection is corrected. More specifically, the injection timing of the intake stroke injection set in step 11 is corrected toward the leading side (TDC side) by α-ΔT.

In step 16, a drive pulse signal having a pulse width corresponding to a separately determined fuel injection amount is supplied to the #n cylinder in the intake stroke at the injection timing set in step 11 and corrected in step 15. Is output to perform fuel injection (the first injection of the intake stroke injection). In step 17, a drive pulse signal having a pulse width corresponding to a separately determined fuel injection amount is output to the # n-1 cylinder during the compression stroke at the injection timing set in step 12, and the fuel injection is performed. (The last injection of the compression stroke injection).

As described above, when switching from the compression stroke injection to the intake stroke injection, as shown in FIG. 4, the injection in the first cylinder (# 1 cylinder) of the intake stroke injection is performed in the last cylinder (in the compression stroke injection). The injection timing of the first cylinder (# 1 cylinder) of the intake stroke injection needs to be corrected to the leading side (TDC side), and it is necessary to perform the injection before the injection of the first cylinder (# 2 cylinder). By making the timing difference between the injection timing of the # 1 cylinder) and the injection timing of the last cylinder (# 2 cylinder) of the compression stroke injection equal to or more than the predetermined value α corresponding to the required charge time, the last stroke of the compression stroke injection is obtained. Cylinder (# 2
(Cylinder) can be injected to avoid misfire. [At the time of switching from intake stroke injection to compression stroke injection] At the time of switching from intake stroke injection to compression stroke injection, the process ends without performing fuel injection in the determination in step 5 (see FIG. 5).

In FIG. 3, steps 2, 3, and 6 correspond to the switching means, steps 7 and 8 correspond to the intake stroke injection means, and steps 9 and 10 correspond to the compression stroke injection. It corresponds to a means. Steps 4, 11 to 17 (particularly step 15) correspond to the switching-time injection timing correction means, and step 15 corresponds to the correction amount setting means.

[0029]

As described above, according to the first aspect of the invention, when switching from compression stroke injection to intake stroke injection in the direct injection spark ignition engine, the first cylinder injection of the intake stroke injection is performed. By correcting at least one of the timing and the injection timing of the last cylinder of the compression stroke injection to increase the difference between these injection timings, the charging time of the fuel injection valve is secured and injection becomes impossible. Can be avoided. Therefore, an effect is obtained that deterioration of drivability and emission due to misfire can be prevented.

According to the second aspect of the present invention, by correcting the injection timing of the first cylinder in the intake stroke injection to the leading side, it is possible to reduce the adverse effect on HC, NOx, and smoke. According to the third aspect of the invention, the difference between the injection timings can be reliably ensured by setting the correction amount such that the difference between the injection timings becomes a predetermined value.

According to the fourth aspect of the invention, the predetermined value is determined by the required charging time of the fuel injection valve,
The required charge time can be secured without excess or shortage.

[Brief description of the drawings]

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

FIG. 2 is a system diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart of injection timing control.

FIG. 4 is a time chart at the time of switching from compression stroke injection to intake stroke injection.

FIG. 5 is a time chart at the time of switching from intake stroke injection to compression stroke injection.

FIG. 6 is a time chart when switching from the conventional compression stroke injection to the intake stroke injection.

[Description of Signs] 1 Engine 2 Combustion chamber 3 Spark plug 8 Fuel injection valve 9 High pressure fuel pump 12 Control unit 13 Crank angle sensor 14 Air flow meter 15 Accelerator sensor

Claims (4)

[Claims] An electromagnetically driven fuel injection valve for directly injecting fuel into a combustion chamber is provided for each cylinder, and a fuel injection timing for each cylinder is set according to an operating state of an engine in either an intake stroke or a compression stroke. Switching means for switching between the cylinders, an intake stroke injection means for driving each fuel injection valve to perform fuel injection in an intake stroke of each cylinder in accordance with an intake stroke injection command from the switching means, and a compression stroke injection command from the switching means. A compression stroke fuel injection means for driving each fuel injection valve in the compression stroke of each cylinder to perform fuel injection, and a fuel injection control device for a direct injection spark ignition type engine. When switching to the intake stroke injection, the injection timing of the first cylinder injected by the intake stroke injection means and the injection timing of the last cylinder injected by the compression stroke injection means A fuel injection control device for a direct-injection spark ignition type engine, comprising: a switching-time injection timing correction means for correcting at least one of the injection timings so as to increase the difference from the timing. 2. When the switching means switches from the compression stroke injection to the intake stroke injection, the injection timing of the cylinder which is first injected by the intake stroke injection means is the last injection timing of the cylinder which is injected by the compression stroke injection means. 2. The switching timing injection timing correction means corrects the injection timing of a cylinder which is first injected by the intake stroke injection means to an advanced side. Fuel injection control device for direct injection spark ignition type engine. 3. The switching time injection timing correction means includes a correction amount setting means for setting a correction amount such that a difference between injection timings becomes a predetermined value. Fuel injection control device for direct injection spark ignition type engine. 4. The fuel injection control device for a direct injection spark ignition engine according to claim 3, wherein the predetermined value is determined by a required charging time of the fuel injection valve.