JP2001107758A - Cylinder fuel injection type spark ignition internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration in a combustion and exhaust emission by forming a favorable homogeneous mixture in a cylinder, even in an engine cooling time, in a cylinder fuel injection type spark ignition internal combustion engine enforcing a homogeneous combustion. SOLUTION: A homogeneous combustion jetting a fuel in an intake stroke mainly is enforced and the valve opening timing of an intake valve is slower than the valve closing timing of an exhaust valve and is after an intake upper dead point (step 103) and a fuel injection is started within the term from the valve closing timing of the exhaust valve to the valve opening timing of the intake valve at the homogeneous combustion time (step 105).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection spark ignition internal combustion engine.

[0002]

2. Description of the Related Art A direct injection type spark ignition internal combustion engine having a fuel injection valve for injecting fuel directly into a cylinder is known. Such an in-cylinder injection spark ignition internal combustion engine,
Since all of the injected fuel is reliably supplied into the cylinder, the fuel injection rate for each engine operating state can be minimized and the fuel consumption rate can be reduced.

[0003] In the cylinder injection type spark ignition internal combustion engine disclosed in Japanese Patent Application Laid-Open No. 9-280092, fuel is not injected after the intake valve is closed when fuel is injected in the intake stroke to perform homogeneous combustion. In this way, by bringing all the injected fuel into sufficient contact with the intake air flow introduced into the cylinder, the vaporization of the fuel is promoted, and the mixing of the vaporized fuel and the intake air is promoted. It is intended to form

[0004]

In the above-mentioned prior art, particularly when the engine is cold when the fuel vaporization state deteriorates,
Just bringing the injected fuel into contact with the normal intake flow
Since the vaporization of the fuel cannot be sufficiently promoted and a desired homogeneous mixture is not formed, the homogeneous combustion and the exhaust emission at this time deteriorate.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cylinder injection type spark ignition internal combustion engine that performs homogeneous combustion, by forming a good homogeneous mixture in the cylinder even when the engine is cold, to perform combustion and exhaust. It is to prevent emission deterioration.

[0006]

According to a first aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine which performs a homogeneous combustion in which fuel is mainly injected in an intake stroke, and an opening timing of an intake valve is adjusted. The fuel injection is started after the intake top dead center later than the closing timing of the exhaust valve, and during the homogeneous combustion, fuel injection is started within a period from the closing timing of the exhaust valve to the opening timing of the intake valve. .

According to a second aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine according to the first aspect, wherein the fuel is injected within the period during the homogeneous combustion. Is terminated.

According to a third aspect of the present invention, there is provided a direct injection type spark ignition internal combustion engine according to the first aspect, wherein the direct injection type spark ignition internal combustion engine is provided. The present invention is characterized in that the combustion is switched between the homogeneous combustion and the stratified combustion in accordance with the operating state of the engine.

According to a fourth aspect of the present invention, there is provided a cylinder injection type spark ignition internal combustion engine according to the third aspect, wherein the valve opening timing of the intake valve is variable. The variable means, and by the variable means,
At the time of the homogeneous combustion, the opening timing of the intake valve is later than the closing timing of the exhaust valve after the intake top dead center, and at the time of stratified combustion, the opening timing of the intake valve is advanced as compared with the time of the homogeneous combustion. It is characterized by the following.

According to a fifth aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine according to the first aspect, wherein the valve opening timing of the intake valve is variable. A variable means for performing the opening of the intake valve by the variable means after the intake top dead center later than the closing time of the exhaust valve during a cold state during the homogeneous combustion, and closing the exhaust valve. Fuel injection is started during the period from the timing to the opening timing of the intake valve, and the opening timing of the intake valve is advanced at the time of the homogeneous combustion in a warm state compared to the cold state during the homogeneous combustion. And

According to a sixth aspect of the present invention, there is provided a cylinder injection type spark ignition internal combustion engine according to the first aspect, wherein at least two adjacent intake valves are adjacent to each other. An intake air amount varying means is provided which is capable of making the intake air amount introduced into the cylinder through the two intake valves different from each other.

[0012]

FIG. 1 is a schematic longitudinal sectional view showing a first embodiment of a direct injection type spark ignition internal combustion engine according to the present invention. In the figure, 1 is an intake port, and 2 is an exhaust port. The intake port 1 communicates with the cylinder via an intake valve 3, and the exhaust port 2 communicates with the cylinder via an exhaust valve 4.
Reference numeral 5 denotes a piston, reference numeral 6 denotes a spark plug disposed substantially at the center of the upper portion of the cylinder, and reference numeral 7 denotes a fuel injection valve for directly injecting fuel from the periphery of the upper portion of the cylinder into the cylinder. Fuel injection valve 7
Is disposed on the intake port 1 side where the temperature becomes relatively low due to the intake air flow in the combustion chamber in order to prevent fuel vapor.

FIG. 2 is a plan view of the piston 5. As shown in FIGS. 1 and 2, a concave cavity 8 is formed on the top surface of the piston 5. The cavity 8 contains the piston 5
It is unevenly distributed on the side of the fuel injection valve 7 on the top surface. Fuel injection valve 7
Has a slit-shaped injection hole, and injects fuel in a thin fan shape. In order to perform stratified combustion, fuel is injected into a cavity 8 formed on the top surface of the piston 5 at the end of the compression stroke, as shown in FIGS.
Although the fuel immediately after the injection indicated by oblique lines is in a liquid state, it proceeds along the bottom wall 8a of the cavity 8 and is vaporized before being guided to the vicinity of the ignition plug 6 by the side wall 8b of the cavity 8 opposed to the fuel injection valve. Is a flammable mixture having good ignitability indicated by dots. Thus, by forming the combustible air-fuel mixture only in the vicinity of the ignition plug 6, stratified charge combustion capable of burning a lean air-fuel mixture in the entire cylinder can be realized.

The fan-shaped fuel spray having a small thickness spreads in the width direction as it travels along the bottom wall 8a of the cavity 8, so that it can absorb heat well from a wide range of the bottom wall 8a of the cavity 8. Can be. In the fuel spread in the width direction on the bottom wall 8 a of the cavity 8, a velocity component which is directed upward is given to the fuel central portion by the side wall 8 b facing the fuel injection valve of the cavity 8, and moves toward the vicinity of the ignition plug 6, and the fuel has both sides. Collides with the fuel injection valve-facing side wall 8b of the cavity 8, which is formed in an arc shape in a plan view of the piston, at an acute angle, so that an upward velocity component and a central velocity component are also imparted. , Toward the spark plug 6. In this manner, the fan-shaped fuel spray having a small thickness is smaller than that of the conventional conical fuel spray.
A good combustible mixture having a degree of vaporization can be formed in the vicinity. In the stratified combustion, a lean air-fuel mixture can be burned as a whole in the cylinder, so that the fuel consumption rate can be reduced. By using the fan-shaped fuel spray having a small thickness, it is possible to increase the fuel injection amount during such stratified combustion, and it is possible to expand the operation region in which the stratified combustion can be performed to a higher load side.

However, when a large amount of fuel is required due to a high engine load, it is difficult to inject fuel only at the end of the compression stroke, and the fuel is injected during the intake stroke to perform homogeneous combustion. It has become. In the homogeneous combustion, the fuel injected in the intake stroke is vaporized and mixed by contact with the intake air flow to form a homogeneous mixture in the cylinder at the time of ignition. However, when the engine temperature is low, such as before engine warm-up, when the temperature in the cylinder is low, the fuel injected into the cylinder does not vaporize sufficiently in a normal intake air flow, and a good homogeneous mixture is formed at the time of ignition. Can not.

In order to solve this problem, in this embodiment, an electromagnetic or hydraulic actuator 1 is used instead of a general cam to drive the intake valve 3 and the exhaust valve 4.
0,11 are used. Such actuators 10 and 11 make it possible to arbitrarily change the valve opening timing and the valve closing timing of the intake valve 3 and the exhaust valve 4.

FIG. 3 is a flow chart for controlling the opening timing of the intake valve 3 by the actuator 10 of the intake valve 3 and the fuel injection timing by the fuel injection valve 7. First, in step 101, it is determined whether or not the current engine operation state determined by the engine load determined by the depression amount of the accelerator pedal and the like, the engine speed, the cooling water temperature, and the like is in a homogeneous combustion region where homogeneous combustion should be performed. Is determined. When this determination is denied, it is the stratified combustion region where stratified combustion is to be performed, and the routine proceeds to step 104, and as described above, the necessary amount of fuel is compressed to form a combustible mixture near the ignition plug 6. It is injected in the latter half of the stroke. At this time, the valve opening timing of the intake valve 3 is set before the intake top dead center, and a valve overlap suitable for the engine operating state is realized between the intake valve 3 and the exhaust valve closing timing after the intake top dead center. It has become so.

On the other hand, when the determination in step 101 is affirmative, that is, when the current engine operating state is in the homogeneous combustion region, the routine proceeds to step 102, where the current cooling water temperature THW is set to the lower limit value THW 'when the engine is warm. It is determined whether or not this is the case. When the determination is affirmative, the routine proceeds to step 106, where a required amount of fuel is injected after the intake valve 3 is opened in the intake stroke. At this time, as shown in FIG.
1 and a valve overlap suitable for the engine operating state is realized between the exhaust valve 4 and the valve closing timing ECT after the intake top dead center. Of course, the opening timing ITO1 of the intake valve 3 and the closing timing ECT of the exhaust valve 4 shown in FIG.
Is an example, and is changed for each engine operating state so as to realize an optimal valve overlap.

At the time of engine warm, the temperature in the cylinder is relatively high, and the fuel injected into the cylinder is easily vaporized. At this time, the valve opening timing of the intake valve 3 is set before the intake top dead center, and as shown by the solid line in FIG. , And does not become so fast, but during the engine warm period, the fuel injected after the intake valve 3 is opened is
This intake flow also allows sufficient vaporization and mixing, and a good homogeneous mixture can be formed at the time of ignition.

On the other hand, when the determination in step 102 is negative, that is, when the engine is cold, step 103
, And the opening timing of the intake valve 3
1 is retarded to ITO2 after the closing timing of the exhaust valve 4.
Next, at step 105, the closing timing E of the exhaust valve 4
Fuel injection is started within a period T from CT to the opening timing ITO2 of the intake valve 3 at this time.

In this manner, when the engine is cold, as shown by the dotted line in FIG. 4, the intake air is not introduced into the cylinder even after passing the intake top dead center, while the pressure in the cylinder increases from the closing of the exhaust valve 4. The pressure drops rapidly, and a large negative pressure is generated before the intake valve 3 opens. The fuel injected at this time is easily vaporized physically by the negative pressure. Furthermore, due to the large negative pressure generated in the cylinder, a very high-speed intake flow is generated in the cylinder at the same time as the opening of the intake valve 3, and the vaporization of the injected fuel is further sufficiently promoted by the intake flow. At the same time, sufficient mixing of the vaporized fuel and the intake air is realized, and a good homogeneous air-fuel mixture can be formed when the engine is cold.

However, if the opening timing of the intake valve 3 is set to be after the closing timing of the exhaust valve 4, a pumping loss is generated due to the negative pressure generated in the cylinder, and the fuel consumption rate is deteriorated. Thus, as in the present embodiment, when the engine is warm during stratified combustion and homogeneous combustion, the intake valve 3
By setting the valve opening timing before the exhaust valve 4 closes, it is possible to prevent the fuel consumption rate from deteriorating at this time.

When the intake valve 3 and the exhaust valve 4 are driven by a normal cam, the opening timing of the intake valve 3 is determined by the exhaust valve 4.
The engine is fixed after the top dead center of the intake later than the closing timing of the engine and the fuel injection is started during the period from the closing of the exhaust valve to the opening of the intake valve, so that the exhaust emission in the homogeneous combustion when the engine is cold It is also possible to give priority to prevention of deterioration. In this case, even in homogeneous combustion at the time of engine warming, vaporization and mixing of the injected fuel is promoted, a more favorable homogeneous mixture can be formed, and the combustion and exhaust emissions at this time can be further improved. . Further, in stratified charge combustion, since sufficient intake air is introduced into the cylinder during the intake stroke, there is no particular problem except for a slight decrease in fuel consumption rate due to pumping loss.

If the opening timing of the intake valve 3 is later than the closing timing of the exhaust valve 4 and later than the intake top dead center, during homogeneous combustion, the closing of the exhaust valve 4 It is preferable to inject all the required amount of fuel within a period until the valve is opened, that is, it is preferable to end the fuel injection within this period. However, when the required amount of fuel according to the engine operating state is relatively large, if most of the fuel is injected within this period, it is sufficiently good even if the fuel injection ends after the intake valve 3 is opened. A homogeneous mixture can be formed in the cylinder.

In the control of the opening timing of the intake valve 3, it is possible to use a variable valve mechanism capable of changing the opening timing of the intake valve 3 in at least two stages. However, when the valve opening timing of the intake valve 3 can be changed in a stepless manner as in the present embodiment, when the engine is warm during stratified charge combustion and homogeneous charge combustion, the valve overload corresponding to the engine operating state is reduced. It is possible to optimize the lap and, for example, when the engine is cold during homogeneous combustion, the opening timing of the intake valve 3 can be greatly delayed from the closing timing of the exhaust valve 4 as the cooling water temperature is lower. It is. As indicated by the dotted line in FIG. 4, as the retard amount increases, the negative pressure generated in the cylinder increases, and the intake flow velocity generated when the intake valve 3 is opened increases. As a result, as the vaporization state of the injected fuel deteriorates, the negative pressure generated in the cylinder is increased and the intake flow velocity at the time of opening the intake valve 3 is increased, so that the vaporized mixture of the injected fuel can be surely mixed. Also, it is possible to prevent an unnecessary increase in pumping loss.

If the opening timing of the intake valve 3 is later than the closing timing of the exhaust valve 4 and later than the intake top dead center, during homogeneous combustion, the high-speed intake flow immediately follows the end of fuel injection. It is advantageous to vaporize and mix the injected fuel to form a favorable homogeneous mixture, that is, it is preferable to start the fuel injection so that the fuel injection ends immediately before the intake valve 3 is opened. In such a fuel injection period, the negative pressure in the cylinder also becomes maximum, and the fuel vaporization by the negative pressure is promoted.
Furthermore, according to such fuel injection, at the time of injection start, the piston is in a relatively lowered position,
Since the distance between the injection hole of the fuel injection valve and the top surface of the piston is relatively large, the injected fuel is less likely to adhere to the top surface of the piston, so that the fuel is also easily vaporized.

FIG. 5 is a bottom view of the cylinder head.
As shown in FIG. 1, the present embodiment is of a two-intake / exhaust type, in which two intake ports 1a and 1b communicate with the inside of a cylinder via two intake valves 3. An intake amount control valve 20 is disposed in one intake port 1b. When the intake amount control valve 20 is fully opened, substantially the same amount of intake air is introduced into the cylinder from the two intake ports 1a and 1b. It is supposed to be.

When homogeneous combustion is performed at high engine speed and high load, the intake air quantity control valve 20 is fully opened and two intake ports 1a and 1b are used to reduce pumping loss and increase volumetric efficiency. As a result, a large amount of intake air is introduced into the cylinder.

However, during homogeneous combustion, when the engine speed is low or the engine load is low, the effect on the increase in pumping loss is small. Therefore, the intake air amount control valve is rotated in the valve closing direction according to the required intake air amount. . As a result, the amount of intake air passing through the two intake ports 1a and 1b becomes uneven, and the two intake flow rates introduced into the cylinders when the two intake valves 3 open are greatly different. As a result, the intake air flow generated in the cylinder becomes a swirl flow, causing strong turbulence in the cylinder and promoting the vaporization and mixing of fuel injected into the cylinder during homogeneous combustion, thereby forming a good homogeneous mixture. Make it easier.

In this way, especially when the opening timing of the intake valve is retarded during the cold period of the engine during homogeneous combustion, a stronger intake flow (swirl flow) is generated in the cylinder when the intake valve is opened. The fuel injected before the opening of the intake valve due to the very strong turbulence generated in the cylinder
Further, the mixture can be sufficiently vaporized and mixed, so that a homogeneous mixture can be more preferably formed in the cylinder.

In the present embodiment, in order to generate strong turbulence in the cylinder, the two intake valves 3 are rotated by rotating the intake amount control valve 20 provided on one intake port 1b in the valve closing direction. Although the intake air amount introduced into the cylinder via the intake air is made different from each other according to the required intake air amount, the valve lift of one intake valve 3 may be reduced by the actuator 10 as a matter of course.

[0032]

As described above, according to the in-cylinder injection spark ignition internal combustion engine of the present invention, in homogeneous combustion in which fuel is mainly injected in the intake stroke, the opening timing of the intake valve is determined by the closing timing of the exhaust valve. Since the fuel injection is started later after the intake top dead center and the fuel injection is started during the period from the closing timing of the exhaust valve to the opening timing of the intake valve, the injected fuel is injected into the cylinder at this time. The generated negative pressure makes it easy to vaporize physically, and at the same time as the opening of the intake valve, the gas is sufficiently vaporized and mixed by the high-speed intake air flow formed in the cylinder due to the negative pressure. Even in this case, a good homogeneous air-fuel mixture can be formed in the cylinder, and the deterioration of combustion and exhaust emissions at this time can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic in-cylinder longitudinal sectional view showing an embodiment of a direct injection type spark ignition internal combustion engine according to the present invention.

FIG. 2 is a plan view of a piston top surface in the in-cylinder injection spark ignition internal combustion engine of FIG. 1;

FIG. 3 is a flowchart showing control of an intake valve opening timing and a fuel injection timing.

FIG. 4 is a graph showing changes in the in-cylinder pressure and the intake flow velocity with a change in the opening timing of the intake valve.

FIG. 5 is a bottom view of a cylinder head in the in-cylinder injection spark ignition internal combustion engine of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intake port 2 ... Exhaust port 3 ... Intake valve 4 ... Exhaust valve 5 ... Piston 6 ... Spark plug 7 ... Fuel injection valve 8 ... Cavity 10, 11 ... Actuator

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/06 335 F02D 41/06 335Z 43/00 301 43/00 301J 301Z (72) Inventor Nobuhiko Koga Aichi No. 1 Toyota Town, Toyota City, Toyota Prefecture F-term (reference) in Toyota Motor Corporation DA12 DA14 DE03S EA02 EA03 EA04 EA11 FA15 FA25 GA02 HA13X HB02X HE01Z HE06Z HE08Z HF08Z 3G301 HA01 HA04 HA09 HA10 HA16 HA17 HA19 JA02 JA21 KA05 KA21 LA07 LB04 LC01 LC08 MA19 MA20 NE06 NE11 NE12 PEB05Z08 PE01

Claims (6)

[Claims] 1. A homogeneous combustion in which fuel is mainly injected in an intake stroke is performed, and an opening timing of an intake valve is later than a closing timing of an exhaust valve and after the intake top dead center. A cylinder injection type spark ignition internal combustion engine, wherein fuel injection is started during a period from a valve closing timing to a valve opening timing of the intake valve. 2. The in-cylinder injection spark ignition internal combustion engine according to claim 1, wherein the fuel injection is terminated within the period during the homogeneous combustion. 3. The cylinder injection type spark according to claim 1, wherein the cylinder injection type spark ignition internal combustion engine switches between the homogeneous combustion and the stratified combustion in accordance with an engine operating state. Ignition internal combustion engine. 4. A variable means for varying the opening timing of the intake valve, wherein the variable means causes the opening timing of the intake valve to be later than the closing timing of the exhaust valve during the homogeneous combustion. The in-cylinder injection spark ignition internal combustion engine according to claim 3, wherein after the dead center, the valve opening timing of the intake valve is advanced during the stratified combustion as compared with the homogeneous combustion. 5. A variable means for changing a valve opening timing of the intake valve, wherein the variable means changes the valve opening timing of the exhaust valve to the valve closing timing of the exhaust valve when the homogeneous combustion is cold. Later, after the intake top dead center, fuel injection is started during the period from the closing timing of the exhaust valve to the opening timing of the intake valve. 2. The cylinder injection type spark ignition internal combustion engine according to claim 1, wherein the valve opening timing of the intake valve is advanced. 6. At least two intake valves adjacent to each other are provided, and there is provided intake amount variable means for making it possible to make intake amounts introduced into a cylinder through the two intake valves different from each other. The in-cylinder injection spark ignition internal combustion engine according to claim 1, wherein: