JP2005214039A - Control device for direct spark ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve combustion stability (flame propagation promotion) by intensifying disturbance in a cylinder due to fuel atomization in ATDC ignition for early activation of a catalyst and HC reduction. <P>SOLUTION: When the warm-up of the catalyst is required, an ignition timing is set after a compression top dead center (TDC). Fuel injection is performed after the TDC but before the ignition timing (Embodiment 1). Otherwise, prior to the fuel injection after the TDC, fuel injection is performed during an intake or compression stroke (Embodiments, 2, 3). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control device for a direct injection spark ignition internal combustion engine, and particularly suitable control when warming-up (activation) of an exhaust purification catalyst provided in an exhaust passage is required, such as immediately after a cold start. Relates to the device.

In Patent Document 1, when the catalyst for exhaust purification is in an unwarmed state lower than the activation temperature, an air-fuel mixture having a partial air-fuel ratio concentration is introduced into the combustion chamber within the period from the intake stroke to the ignition timing. The fuel is injected before the late injection to be formed and the fuel is injected before the late injection, and the air-fuel mixture having a leaner air-fuel ratio than the stoichiometric air-fuel ratio is generated in the combustion chamber. And at least two split injections with the early injection to be performed, and the ignition timing is retarded by a predetermined amount from the MBT, and the ignition timing is set before the compression top dead center in the no-load region of the engine. It is described that the ignition timing is retarded until after the compression top dead center in the low rotation and low load region of the engine except the region.
Japanese Patent No. 3325230

  In order to accelerate the afterburning for early activation of the catalyst and reduction of HC when the engine is cold, the retard of the ignition timing is effective. To obtain a greater effect, ignition after compression top dead center (ATDC ignition) ) Is desirable, but in order to perform stable combustion with ATDC ignition, it is necessary to shorten the combustion period. For this purpose, the turbulence in the cylinder is strengthened and the combustion speed (flame propagation speed) is increased. is required. Therefore, it is conceivable that turbulence is generated in the cylinder by the fuel spray injected at a high pressure.

  However, in Patent Document 1, the first fuel injection (early injection) is mainly performed during the intake stroke, and the second fuel injection (late injection) is performed at 120 to 45 ° BTDC in the compression stroke. If the last fuel injection is before TDC, even if turbulence is generated in the cylinder by the spray, the turbulence attenuates after TDC, and does not contribute to the increase in flame propagation speed by ATDC ignition.

For this reason, ATDC ignition is more advantageous for exhaust temperature rise and HC reduction, but since combustion stability is not established, in Patent Document 1, BTDC ignition is used in the no-load region.
The present invention has been made in view of such a situation, and an object thereof is to improve combustion stability in ATDC ignition for early activation of a catalyst and HC reduction.

  For this reason, the present invention is configured such that when the catalyst is required to be warmed up, the ignition timing is set after the compression top dead center, while the fuel is injected after the compression top dead center and before the ignition timing.

  According to the present invention, on the ATDC side, turbulence generated in the intake stroke and compression stroke is attenuated, but by generating and strengthening in-cylinder turbulence by fuel injection in the expansion stroke after TDC, ATDC ignition is performed. The flame propagation can be promoted. Therefore, when realizing ATDC ignition for obtaining early activation of the catalyst and reduction of HC, the in-cylinder turbulence can be strengthened and the combustion stability can be improved.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an engine (direct injection spark ignition type internal combustion engine) showing an embodiment of the present invention.
In the intake passage 2 of the engine 1, an electric throttle valve 3 for controlling the intake air amount is installed. The opening degree of the electric throttle valve 3 is controlled by a step motor or the like that is operated by a signal from an engine control unit (hereinafter referred to as ECU) 20.

A fuel injection valve 6 is installed in the combustion chamber 4 of the engine 1 together with a spark plug 5.
The fuel injection valve 6 is energized to the solenoid by an injection pulse signal output from the ECU 20 in the intake stroke or the compression stroke in synchronization with the engine rotation, so that the fuel adjusted to a predetermined pressure is injected. It has become. In the case of intake stroke injection, the injected fuel diffuses throughout the combustion chamber 4 to form a homogeneous mixture, and in the case of compression stroke injection, a stratified mixture is concentrated around the spark plug 5. Based on the ignition signal from the ECU 20, the ignition plug 5 is ignited and burned (homogeneous combustion or stratified combustion).

An exhaust purification catalyst 8 is provided in the exhaust passage 7 of the engine 1.
The ECU 20 detects the accelerator opening APO detected by the accelerator pedal sensor 21, the engine speed Ne detected by the crank angle sensor 22, the intake air amount Qa detected by the hot-wire air flow meter 23, and the throttle sensor 24. The throttle opening TVO and the engine coolant temperature Tw detected by the water temperature sensor 25 are input.

  The ECU 20 sets a combustion method (homogeneous combustion, stratified combustion) based on the engine operating conditions detected from these input signals, and according to this, the opening degree of the electric throttle valve 3 and the fuel injection valve 6 The fuel injection timing, the fuel injection amount, and the ignition timing of the spark plug 5 are controlled. Note that, under normal operating conditions (after completion of warm-up), stratified combustion is performed with extremely lean A / F = about 30 to 40 (stratified lean combustion). Homogeneous combustion includes homogeneous lean combustion (A / F = 20-30) and homogeneous stoichiometric combustion.

The present invention realizes optimal combustion control for this when the warm-up of the catalyst 8 is required, such as immediately after a cold start, and this is performed by the ECU 20 according to the flowchart of FIG.
A flow chart of the catalyst warm-up request control in FIG. 2 will be described.
In S1, it is determined whether or not the catalyst 8 is activated. Specifically, when a catalyst temperature sensor is provided, the catalyst temperature is detected by this. If the catalyst temperature sensor is not provided, the catalyst temperature is estimated from the cooling water temperature Tw. Alternatively, the catalyst temperature is estimated based on the cooling water temperature at the start and the integrated value of the intake air amount after the start. Then, it is determined whether or not the detected or estimated catalyst temperature is equal to or higher than a predetermined activation temperature.

If the catalyst is not activated, the process proceeds to S2.
In S2, as the catalyst warm-up request control, the ignition timing is retarded until after the compression top dead center (TDC). Specifically, the ignition timing is set to 15 to 30 ° ATDC (for example, 20 ° ATDC), and ATDC ignition is performed. Further, the fuel injection timing is set after the compression top dead center (TDC) and before the ignition timing, and is set as the expansion stroke injection (ATDC injection) after the TDC. The fuel injection may be divided into two, and the second fuel injection may be ATDC injection, and the intake stroke injection or the compression stroke injection may be performed as the first fuel injection preceding this. Details of the fuel injection will be described later. Further, the air-fuel ratio in the combustion chamber by fuel injection (when fuel injection is divided into two times, the air-fuel ratio in the combustion chamber by two fuel injections) is stoichiometric to slightly lean (A / F = 16 to 17). To do.

After S2, the process returns to S1. When the catalyst 8 is activated by the catalyst warm-up request control, the process proceeds from S1 to S3 and shifts to normal control. In normal control, the above-described stratified lean combustion, homogeneous lean combustion, homogeneous stoichiometric combustion, and the like are performed according to operating conditions.
Next, the catalyst warm-up request control will be described in detail.
In order to promote catalyst warm-up and reduce HC when the engine is cold, ignition timing delay is effective, and ignition after TDC (ATDC ignition) is desirable.

In order to perform stable combustion with ATDC ignition, it is necessary to shorten the combustion period. For this purpose, flame propagation due to turbulence must be promoted.
In order to promote flame propagation, it is necessary to increase the turbulence after the ignition timing. However, referring to FIG. 3, for example, a gas flow control valve (for example, a tumble control valve) disposed in the intake port is operated to perform an intake stroke. The turbulence generated in Fig. 3A attenuates with the progress of the compression stroke, and the turbulence temporarily increases due to the collapse of the tumble flow by the piston in the latter half of the compression stroke (Fig. 3B), but attenuates after TDC. As a result (FIG. 3C), combustion improvement (improving flame propagation) using the turbulence cannot be expected so much.

Therefore, in the present invention, in the case of ATDC ignition, fuel injection (ATDC injection) is performed before the ignition timing after TDC, and the gas flow is strengthened after TDC by using turbulence caused by high-pressure fuel injection. To improve combustion (improving flame propagation).
Specifically, as shown in the first embodiment of FIG. 4, the fuel is injected after the TDC in the expansion stroke before the ignition timing.

  Further, in the second embodiment of FIG. 4, the fuel injection is divided into two times, the first fuel injection is performed in the intake stroke, and the second fuel injection is set as ATDC injection. Thus, if fuel injection is performed during the intake stroke prior to ATDC injection (expansion stroke injection), in the intake stroke injection, the turbulence due to the fuel spray is attenuated in the latter half of the compression stroke, and this enhances gas flow in the ATDC. Has little effect, but the injected fuel is diffused throughout the combustion chamber and contributes to the promotion of afterburning by ATDC ignition, which is effective in reducing HC and increasing exhaust temperature.

  Further, in Example 3 of FIG. 4, the fuel injection is divided into two times, the first fuel injection is performed in the compression stroke, and the second fuel injection is set as ATDC injection. Thus, if fuel injection is performed during the compression stroke prior to ATDC injection (expansion stroke injection), the compression stroke injection is slower to attenuate the disturbance due to the fuel spray than the intake stroke injection. The turbulence caused by the first fuel injection remains, and by performing the second fuel injection after TDC, the turbulence can be strengthened to promote the turbulence generated by the first fuel injection, and further gas flow enhancement in ATDC I can plan.

In this case, the first compression stroke injection may be performed in the first half of the compression stroke, but if performed in the second half of the compression stroke (after 90 ° BTDC), the disturbance can be further increased. In particular, if the first compression stroke injection is performed after 45 ° BTDC, more preferably after 20 ° BTDC, the gas flow after TDC can be further strengthened.
According to this embodiment, when the catalyst needs to be warmed up, the ignition timing is set to ATDC, while fuel is injected before TIG and after TDC, thereby generating in-cylinder turbulence immediately before ignition. -It is possible to enhance the combustion stability (acceleration of flame propagation) when realizing ATDC ignition for obtaining early activation of the catalyst and reduction of HC.

Further, according to this embodiment, by setting the ignition timing to 15 to 30 ° ATDC, a sufficient afterburning effect for early activation of the catalyst and reduction of HC can be obtained. In other words, even if the ignition timing is delayed, the fuel injection is delayed until just before that, and the generation point of the turbulence is also delayed, so that the combustion improvement by improving the flame propagation can be achieved.
Further, according to the present embodiment, fuel injection is performed during the intake stroke prior to fuel injection after TDC, so that the injected fuel is diffused throughout the combustion chamber by ignition, and afterburning is promoted by ATDC ignition. This contributes to reducing HC and increasing exhaust temperature.

In addition, according to the present embodiment, prior to fuel injection after TDC, fuel injection is performed during the compression stroke, whereby turbulence is promoted by the first fuel injection, thereby further enhancing gas flow in ATDC.
Further, according to the present embodiment, the air-fuel ratio in the combustion chamber by fuel injection is stoichiometric to slightly lean (A / F = 16 to 17), so that oxygen necessary for afterburning is necessary and sufficient. Afterburning can be promoted.

  Although fuel injection in the ATDC is performed before the ignition timing, flame propagation proceeds with time, so that the end of fuel injection may be later than the ignition timing in time for flame propagation.

Engine system diagram showing an embodiment of the present invention Control flow chart Explanatory drawing of in-cylinder turbulence when using a gas flow control valve in the intake port Illustration of fuel injection timing

Explanation of symbols

1 engine
2 Intake passage
3 Electric throttle valve
4 Combustion chamber
5 Spark plug
6 Fuel injection valve
7 Exhaust passage
8 Catalyst
20 ECU
21 Accelerator pedal sensor
22 Crank angle sensor
23 Air Flow Meter
24 Throttle sensor
25 Water temperature sensor

Claims (5)

  When warming-up of an exhaust purification catalyst arranged in the exhaust passage is required, the ignition timing is set after the compression top dead center, while the fuel is injected after the compression top dead center and before the ignition timing. A direct-injection spark-ignition internal combustion engine control device.   2. The control device for a direct injection spark ignition type internal combustion engine according to claim 1, wherein the ignition timing is set to 15 to 30 [deg.] After compression top dead center.   3. The control device for a direct injection spark ignition type internal combustion engine according to claim 1, wherein fuel injection is performed during an intake stroke prior to fuel injection after compression top dead center.   3. The control device for a direct injection spark ignition type internal combustion engine according to claim 1, wherein fuel injection is performed during a compression stroke prior to fuel injection after compression top dead center.   The control apparatus for a direct injection spark ignition type internal combustion engine according to any one of claims 1 to 4, wherein the air-fuel ratio in the combustion chamber by fuel injection is stoichiometric to slightly lean.

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