JP2003090249A - Spark ignition type direct injection internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve torque by suppressing generation of knocking, in a low rotation and high load region. SOLUTION: In an operating region in which low rotation and a high load are generated, a fuel injection amount is set so as to generate a mixture of stoic or rich as a total unit in a combustion chamber. In the case of injecting the set fuel injection amount, dividing it into during an intake stroke and during compression stroke, most part of fuel is injected during the intake stroke.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark ignition type direct injection internal combustion engine for directly injecting fuel into a cylinder, and more particularly to a technique for avoiding knocking.

[0002]

2. Description of the Related Art Conventionally, there is known an internal combustion engine in which fuel is divided and injected during an intake stroke and a compression stroke. For example, Japanese Patent Laid-Open No. 10-213744 discloses that in an engine that performs stratified combustion by injecting fuel during a compression stroke in a specific operation region at medium and high loads, the intake stroke is performed prior to fuel injection during the compression stroke. Discloses a technique of injecting an amount of fuel that cannot self-ignite.

Further, in Japanese Unexamined Patent Publication (Kokai) No. 10-212987, when the catalyst is cold when the temperature is lower than the activation temperature, fuel is divided into an intake stroke and a compression stroke and injected, so that the stoichiometric air-fuel ratio or A technique of forming a rich air-fuel mixture and forming a lean air-fuel mixture around the air-fuel mixture is disclosed.

[0004]

However, although the former can increase the torque while avoiding knocking, most of the set fuel (60 to 90%) is injected in the latter half of the compression stroke, so that the air-fuel mixture is mixed. Since the mixing time is short and the air-fuel mixture around the spark plug becomes too rich, the unburned fuel discharge and smoke discharge may increase.

Further, when the engine is continuously operated under the operating condition of exhausting smoke, carbon deposits are accumulated in the combustion chamber, and the substantial compression ratio of the engine is increased to deteriorate the knocking resistance performance in the long term (that is, Engine torque will be reduced). On the other hand, the latter controls the injection amount during the intake stroke to be larger than the injection amount during the compression stroke, but it is intended to warm up the catalyst when the engine is cold, where knocking is unlikely to occur, and avoids knocking. It is a technology unrelated to control.

The present invention has been made in order to solve the above conventional problems, and effectively suppresses knocking and improves torque in a low rotation and high load region where knocking easily occurs. An object of the present invention is to provide a spark ignition type direct injection internal combustion engine that can be performed.

[0007]

Therefore, in the invention according to claim 1, the fuel injection amount is set so that the air-fuel mixture in the entire combustion chamber becomes stoichiometric or rich in the operating region where the rotation speed is low and the load is high. However, when the set fuel injection amount is divided and injected during the intake stroke and the compression stroke, more fuel is injected during the intake stroke than during the compression stroke.

According to a second aspect of the present invention, the amount of fuel injected during the intake stroke is 90% of the set fuel injection amount.
% Or more. The invention according to claim 3 controls the amount of fuel injected during the compression stroke and the injection timing to make the equivalence ratio of the air-fuel mixture formed around the spark plug larger than 1.0 and smaller than 1.2. It is characterized by doing.

According to a fourth aspect of the present invention, the volume of the air-fuel mixture formed around the spark plug is controlled to be half or less of the combustion chamber volume by controlling the amount of fuel injected and the injection timing during the compression stroke. Is characterized by. The invention according to claim 5 is characterized in that the fuel amount injected during the compression stroke is set to be larger as the rotational speed of the engine is lower.

The invention according to claim 6 is characterized in that the injection timing during the compression stroke is set to be slower as the rotational speed of the engine is higher.

[0011]

According to the invention of claim 1, the low rotation speed
Under operating conditions where knocking is likely to occur, such as in the high load region, the fuel set so that the air-fuel mixture in the combustion chamber becomes stoichiometric or rich is injected separately during the intake stroke and the compression stroke. .

As a result, the peripheral air-fuel mixture in the combustion chamber is made lean, the knocking resistance is improved, and the ignition timing can be advanced, so that the torque can be improved. Here, by injecting more fuel during the intake stroke than during the compression stroke, the mixture (rich mixture) around the spark plug formed by the injection during the compression stroke becomes too rich. By avoiding the above, it is possible to prevent a decrease in torque due to an increase in unburned fuel, and deterioration of fuel efficiency and exhaust performance.

According to the second aspect of the present invention, the amount of fuel injected during the intake stroke is 90% or more of the total fuel injection amount set. As a result, it is possible to reliably prevent a situation in which the rich air-fuel mixture becomes too rich, and it is possible to reliably obtain the torque improving effect by improving the knocking resistance performance.

According to the third aspect of the present invention, the equivalence ratio of the air-fuel mixture formed around the spark plug is made larger than 1.0 by controlling the amount of fuel injected and the injection timing during the compression stroke. Make it smaller than 1.2. As a result, smoke discharge can be reliably prevented, the maximum torque can be increased more than that during normal homogeneous combustion, and fuel split injection can be effectively performed.

According to the invention of claim 4, by controlling the amount of fuel injected during the compression stroke and the injection timing, the volume of the air-fuel mixture formed around the spark plug is reduced to less than half the volume of the combustion chamber. To do. As a result, it is possible to suppress the discharge of unburned fuel, increase the maximum torque as compared with the time of normal homogeneous combustion, and execute the fuel split injection effectively.

According to the fifth aspect of the present invention, the amount of fuel injected during the compression stroke is set to be higher as the engine speed is lower, so that the amount of fuel injected during the intake stroke is formed. A relatively lean air-fuel mixture around the combustion chamber can be made leaner. As a result, the knocking resistance can be prevented from deteriorating even in the low rotation region where the time of exposure to high temperature and high pressure becomes long, and the divided injection of fuel can be effectively executed.

According to the sixth aspect of the invention, the injection timing during the compression stroke is set to be slower as the rotational speed of the engine is higher. This is because it has been confirmed by an experiment that the optimum timing of the compression stroke injection is retarded as the engine speed increases, and thus the fuel split injection can be effectively performed.

[0018]

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

A fuel injection valve 11 for directly injecting fuel into the combustion chamber 1 and an ignition plug 12 for spark ignition of a mixture gas in the combustion chamber 1 are arranged in the cylinder head 2 so as to face the combustion chamber 1. Has been done. On the crown surface of the piston 4, the fuel injection valve 1
1 is formed with a recess for transporting the fuel injected by No. 1 around the spark plug 12.

At the open end of the intake port 5 on the combustion chamber 1 side,
An intake valve 7 that is opened and closed by an intake cam 9 is provided, and an exhaust valve 8 that is opened and closed by an exhaust cam 10 is provided at an opening end of the exhaust port 6 on the combustion chamber 1 side. The control unit (C / U) 13 grasps the operating state of the engine based on signals from various sensors (crank angle sensor, air flow meter, accelerator opening sensor, etc.) (not shown), and performs predetermined arithmetic processing. Fuel injection control (injection amount, injection timing) by the fuel injection valve 11 and ignition timing control by the spark plug 12 are performed.

The fuel injection valve 11 has a C / U1
The valve is opened in response to the drive signal from No. 3, and the valve opening timing and time are controlled to inject a set amount of fuel at the set timing. When the fuel is injected during the intake stroke, the injected fuel diffuses to form a homogeneous air-fuel mixture throughout the combustion chamber 1. When the fuel is injected during the compression stroke, the spark plug 12
A concentrated (stratified) mixture can be formed around.

Therefore, by combining the fuel injection control and the air-fuel ratio control, stratified lean combustion, homogeneous lean combustion, homogeneous stoichiometric combustion, etc. are possible, depending on the operating condition of the engine (engine rotation speed, target torque). Either combustion method is set. In the present embodiment, during normal operation, the fuel is injected during the intake stroke in an amount such that the air-fuel mixture has a stoichiometric air-fuel ratio (stoichiometric ratio) to perform homogeneous stoichiometric fuel, and low rotation speed and low load. In the region, stratified lean combustion is performed by injecting an amount of fuel such that the air-fuel mixture of the entire combustion chamber 1 becomes lean during the compression stroke.

Also, low rotation, which tends to cause knocking,
In the high load region, the amount of fuel is set so that the air-fuel mixture in the fuel chamber 1 as a whole becomes stoichiometric or rich, and the fuel is divided and injected during the intake stroke and the compression stroke. By splitting and injecting the fuel set in this way, a homogeneous air-fuel mixture is formed in the combustion chamber 1 by the fuel injection set during the intake stroke, and by the fuel injection set during the compression stroke. A concentrated air-fuel mixture is formed around the spark plug 12.

As a result, as compared with the case where all of the set amount of fuel is injected during the intake stroke (hereinafter referred to as normal homogeneous combustion), only the amount of (the fuel of) the concentrated air-fuel mixture is increased in the combustion chamber. Since the equivalence ratio of the peripheral air-fuel mixture (end gas) in 1 becomes lean, the knocking resistance performance is improved at the full load of the engine. As a result, since the knocking limit ignition timing is also advanced, the set ignition timing can be advanced, and the engine torque can be increased more than when normal homogeneous combustion is performed.

The split fuel injection according to the present invention will be described below. FIG. 2 shows the equivalence ratio of the concentrated air-fuel mixture around the spark plug 12 (rich portion of the stratified air mixture, hereinafter simply referred to as rich air-fuel mixture) formed by the fuel injected during the compression stroke, engine full load torque and smoke. It is a figure which shows the relationship of generation amount, and is calculated | required by experiment.

In FIG. 2, the rich air-fuel mixture occupies the same volume in the combustion chamber 1 with the spark plug 12 as the center, and the intake stroke increases as the equivalence ratio of the rich air-fuel mixture increases (becomes richer). A small amount of fuel is injected inside. That is, the average equivalence ratio of the entire combustion chamber 1 is the same, but the greater the equivalence ratio of the rich mixture, the greater the difference from the relatively lean equivalence ratio of the periphery of the combustion chamber.

As shown in the figure, when the equivalence ratio of the rich air-fuel mixture is increased, unburned fuel increases, so that the engine full load torque decreases and the amount of smoke generation increases. Therefore, in order to effectively execute the split fuel injection,
It is necessary to set the amount of fuel injected during the intake stroke to be larger than the amount of fuel injected during the compression stroke.
Most of the set fuel is injected during the intake stroke, and the remaining fuel is injected during the compression stroke.

When the equivalence ratio of the rich air-fuel mixture is larger than 1.0 and smaller than about 1.2, the engine full load torque normally injects all the set fuel during the intake stroke. Exceeds the torque during homogeneous combustion. Therefore, in the low rotation / high load region where the ignition timing is limited to the retard side due to knocking and the torque decreases, the control unit 13 causes the equivalence ratio of the rich mixture to be larger than 1.0 and smaller than 1.2. The amount of fuel injected during the compression stroke and the injection timing are set so that

This makes it possible to effectively carry out the split injection of fuel while preventing the generation of smoke. That is,
Generally, the maximum torque is higher during normal homogeneous combustion in which all fuel is injected during the intake stroke than when split injection is performed. By executing the divided injection as described above, it is possible to improve the anti-knocking performance and to obtain a torque larger than the maximum torque during normal homogeneous combustion by advancing the ignition timing accordingly.

FIG. 3 is a diagram showing the relationship among the ratio of the rich air-fuel mixture volume, the engine full load torque, and the ratio of the unburned air-fuel mixture to one volume of the combustion chamber, which is obtained by an experiment similar to FIG. is there. In FIG. 3, the average equivalence ratio of the entire combustion chamber 1 and the equivalence ratio of the rich mixture are the same. That is,
As the ratio of the rich air-fuel mixture in the volume of the combustion chamber increases, the difference from the relatively lean equivalence ratio of the peripheral portion of the combustion chamber increases.

As shown in the figure, when the ratio of the rich air-fuel mixture volume to the combustion chamber 1 volume increases, the engine full load torque decreases, and when the rich air-fuel mixture occupies more than half of the combustion chamber 1 volume, the entire engine The load torque is lower than the torque during normal homogeneous combustion. Therefore, in the low rotation / high load region where the ignition timing is limited to the retard side due to knocking and the torque decreases, the control unit 13 compresses the rich mixture volume to half or less of the combustion chamber 1 volume. The amount of fuel injected during the stroke and the injection timing are set.

As a result, it is possible to effectively execute the split injection of fuel while preventing an increase in unburned fuel. Summarizing the above, FIG. 4 shows the relationship between the ratio of the rich mixture to the volume of the combustion chamber, the equivalence ratio of the rich mixture, and the engine full load torque. As shown in the figure, in the low rotation speed / high load region where the torque and fuel consumption deteriorate, 90% or more of the fuel injection amount set according to the operating state of the engine is injected during the intake stroke, and the remaining fuel is injected. It is preferable to set the injection timing during the compression stroke so that the equivalence ratio of the rich mixture formed by the injection is smaller than 1.2 and the volume of the rich mixture is half or less of the volume of the combustion chamber.

In this way, in the low rotation / high load region where knocking is likely to occur, knocking can be avoided while maximizing the torque improving effect by the split injection. Next, the amount of fuel injected during the compression stroke and the injection timing will be described. FIG. 5 shows the relationship between the engine speed and the optimum equivalence ratio of the rich mixture.

The lower the engine speed, the longer the time the ambient air-fuel mixture in the combustion chamber is exposed to high temperature and high pressure, and the lower the knocking resistance. For this reason, it is necessary to increase the degree of stratification toward the lower rotation speed side, and the optimum equivalence ratio of the rich mixture becomes rich. Therefore, the control unit 13 sets a larger amount of fuel to be injected during the compression stroke as the engine speed is lower.

FIG. 6 shows the relationship between the fuel injection timing during the compression stroke (compression stroke injection timing), the engine full load torque, and the engine rotation speed, which was obtained by experiments.
As shown in the figure, the compression stroke injection timing has an optimum injection timing that maximizes the engine full load torque. That is, if the fuel injection during the compression stroke is performed earlier than the optimum injection timing, the stratification degree of the air-fuel mixture decreases and the knocking resistance performance deteriorates. For this reason, the set ignition timing must be retarded, and the engine full load torque is reduced.

On the other hand, if the fuel injection during the compression stroke is performed later than the optimum injection timing, the stratification degree of the air-fuel mixture becomes too strong, the proportion of unburned fuel increases, and smoke is generated. Engine full load torque decreases. It has also been confirmed by experiments that the optimum injection timing is retarded as the engine speed increases.

Therefore, the control unit 13 sets the compression stroke injection timing to the retard side as the engine speed increases.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between a rich equivalence ratio, an engine full load torque, and a smoke generation amount in the embodiment.

FIG. 3 is a diagram showing a relationship among a ratio of a rich mixture volume to a combustion chamber volume, an engine full load torque, and a ratio of an unburned mixture in the embodiment.

FIG. 4 is a diagram showing a relationship between a ratio of a rich mixture to a combustion chamber volume, an equivalence ratio of the rich mixture, and an engine full load torque in the embodiment.

FIG. 5 shows the relationship between the engine speed and the optimum equivalence ratio of the rich mixture in the embodiment.

FIG. 6 is a diagram showing a relationship among a compression stroke injection timing, an engine full load torque, and an engine rotation speed in the embodiment.

[Explanation of symbols]

1 combustion chamber 2 cylinder head 3 cylinder block 4 pistons 5 intake ports 6 exhaust port 7 intake valve 8 exhaust valve 11 Fuel injection valve 12 Spark plug 13 Control unit (C / U)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Jun Terachi             Nissan, Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan             Inside the automobile corporation F-term (reference) 3G023 AA02 AA06 AB01 AC04 AD02                       AD09 AG01                 3G301 HA01 HA04 HA16 JA22 JA24                       KA06 KA08 KA09 KA23 KA24                       KA25 LB04 MA01 MA11 MA18                       MA23 NE12 PA01Z PE03Z                       PF03Z

Claims (6)

[Claims] 1. A fuel injection amount is set so that the air-fuel mixture in the entire combustion chamber becomes stoichiometric or rich in an operating region where low rotation and high load occur, and the set fuel injection amount is set during the intake stroke and the compression stroke. A spark ignition type direct injection internal combustion engine characterized by injecting a larger amount of fuel during an intake stroke than during a compression stroke when the fuel is divided into medium and divided injections. 2. The spark ignition type direct injection internal combustion engine according to claim 1, wherein an amount of fuel injected during the intake stroke is 90% or more of the set fuel injection amount. 3. The equivalence ratio of the air-fuel mixture formed around the spark plug is controlled to be larger than 1.0 and smaller than 1.2 by controlling the amount of fuel injected during the compression stroke and the injection timing. The spark ignition type direct injection internal combustion engine according to claim 1 or 2. 4. The volume of the air-fuel mixture formed around the spark plug is reduced to half or less of the combustion chamber volume by controlling the amount of fuel injected and the injection timing during the compression stroke. The spark ignition type direct injection internal combustion engine according to any one of claims 1 to 3. 5. The spark ignition type direct injection according to claim 1, wherein the fuel amount injected during the compression stroke is set to be larger as the engine speed is lower. Internal combustion engine. 6. The injection timing during the compression stroke is set to be slower as the engine speed is higher.
6. The spark ignition type direct injection internal combustion engine according to claim 5.