JP4207481B2 - In-cylinder injection spark ignition internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection spark ignition internal combustion engine.
[0002]
[Prior art]
An in-cylinder spark-ignition internal combustion engine equipped with a fuel injection valve that directly injects fuel into a cylinder ignites a combustible mixture with good ignitability at the time of ignition by injecting fuel in the latter half of the compression stroke. It is formed only in the vicinity of the plug, and realizes stratified combustion capable of burning a lean air-fuel mixture as a whole in the cylinder.
[0003]
Thus, stratified combustion is effective in reducing the fuel consumption rate, but the fuel injected in the compression stroke must be vaporized in a relatively short time until ignition, and a general in-cylinder injection spark ignition internal combustion engine Then, at high engine loads that require a large amount of fuel, stratified combustion is abandoned, and fuel is injected during the intake stroke, so that homogeneous combustion is formed to form a homogeneous mixture in the cylinder at the time of ignition. Yes.
[0004]
Thus, in a general in-cylinder injection spark ignition internal combustion engine, stratified combustion and homogeneous combustion are switched and executed. In order to realize good homogeneous combustion, it is necessary to generate a strong intake swirl flow such as a tumble flow or a swirl flow in the cylinder in the intake stroke. Strong intake swirl allows the injected fuel to be sufficiently agitated to form a good homogeneous mixture in the cylinder, as well as turbulence in the cylinder at the time of ignition to increase combustion speed And
[0005]
However, if a strong intake swirl flow is generated in the cylinder during the intake stroke and the cylinder is disturbed at the time of ignition, this disturbance inhibits the formation of a combustible mixture near the spark plug during stratified combustion. In addition, the combustible air-fuel mixture formed in the vicinity of the spark plug is dispersed before ignition so that good stratified combustion cannot be realized.
[0006]
As described above, it is desirable to generate a strong intake swirl flow in the cylinder in order to realize good homogeneous combustion, but it is preferable not to generate an intake swirl flow in the cylinder that causes turbulence at the ignition timing during stratified combustion. . In order to satisfy such conflicting requirements, for example, when one of the two intake ports is used as a swirl port and the intake air is supplied into the cylinder, only the swirl port is used when the swirl flow is necessary. It is known to use two intake ports when is not needed. Japanese Patent Laid-Open No. 6-1559079 discloses that when an intake port is divided into a tumble port and a bypass port and the intake air is supplied into the cylinder, only the tumble port is used when a tumble flow is required. It has been proposed to use two ports when tumble flow is not required.
[0007]
[Problems to be solved by the invention]
As described above, it is possible to generate or not generate a strong intake swirl flow in the cylinder, but when this is applied during homogeneous combustion and stratified combustion in a cylinder injection spark ignition internal combustion engine, In order to generate a strong intake swirl flow in the cylinder during homogeneous combustion on the high load side where the required intake amount is relatively large, only the swirl port or the tumble port is used when supplying the intake air into the cylinder. In other words, the total cross-sectional area of the intake port becomes small, and the intake amount becomes insufficient, so that it is impossible to achieve good homogeneous combustion.
[0008]
Accordingly, an object of the present invention is to provide a strong intake swirl flow in the intake stroke without causing a shortage of intake air during homogeneous combustion in a cylinder injection spark ignition internal combustion engine that switches between stratified combustion and homogeneous combustion. It is ensured that it is reliably generated, and such a strong intake swirl flow is not generated in the cylinder during stratified combustion, so that both homogeneous combustion and stratified combustion are good.
[0009]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an in-cylinder injection spark ignition internal combustion engine including an ignition plug, a lift amount variable mechanism of an intake valve, and a fuel injection valve that directly injects fuel into the cylinder. In a cylinder injection spark ignition internal combustion engine that switches between stratified combustion and homogeneous combustion, the intake port allows the maximum amount of intake air in the homogeneous combustion at the time of engine high load to pass and As the intake air amount supplied into the cylinder increases, a stronger intake swirl flow is generated in the cylinder. Unlike the homogeneous combustion, the throttle valve is fully opened during the stratified combustion, and the lift amount variable mechanism be characterized by weakening the intake swirl flow generated in the compared to the homogeneous combustion to reduce the amount of intake air passing through the intake port into the cylinder by reducing the lift amount of the intake valve .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a direct injection 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 the intake valve 3, and the exhaust port 2 communicates with the cylinder via the exhaust valve 4. 5 is a piston, 6 is a spark plug disposed substantially at the center of the cylinder upper part, and 7 is a fuel injection valve for directly injecting fuel from the periphery of the cylinder upper part into the cylinder. The 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.
[0014]
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 is unevenly distributed on the fuel injection valve 7 side on the top surface of the piston 5. The fuel injection valve 7 has a slit-shaped injection hole, and injects the fuel into a thin fan shape. In order to perform stratified combustion, as shown in FIGS. 1 and 2, fuel is injected into a cavity 8 formed on the top surface of the piston 5 in the latter half of the compression stroke. The fuel immediately after the injection indicated by the oblique lines is in a liquid state, but is atomized by friction with the intake air and enters the cavity 8, and then proceeds along the bottom wall 8 a of the cavity 8 to the fuel injection valve of the cavity 8. It vaporizes until it is led to the vicinity of the spark plug 6 by the opposing counter side wall 8b, and at the time of ignition, it becomes a combustible air-fuel mixture having good ignitability indicated by dots. Thus, by forming a combustible air-fuel mixture only in the vicinity of the spark plug 6, it is intended to realize stratified combustion that enables combustion of a lean air-fuel mixture as a whole in the cylinder.
[0015]
The thin fan-shaped fuel spray spreads in the width direction as it travels along the bottom wall 8 a of the cavity 8, and thus can absorb heat well from a wide area of the bottom wall 8 a of the cavity 8. In the fuel that spreads in the width direction on the bottom wall 8a of the cavity 8, the fuel central portion is given an upward velocity component by the opposite side wall 8b of the cavity 8 and is directed to the vicinity of the spark plug 6, and both sides of the fuel are pistons. Each of the opposing side walls 8b of the cavity 8 that has an arc shape in plan view collides at an acute angle, and an upward speed component and a central speed component are also applied to the vicinity of the spark plug 6. Head.
[0016]
Thus, the fan-shaped fuel spray having a small thickness can form a lump of combustible air-fuel mixture having a good degree of vaporization in the vicinity of the spark plug 6 as compared with the conventional conical fuel spray. Thereby, the fuel injection amount at the time of stratified combustion can be increased, and stratified combustion with a low fuel consumption rate can be expanded to the high load side. However, the present invention does not have a fuel injection valve that realizes such a fan-shaped fuel spray as an essential component, and a fuel injection valve that realizes a fuel spray of a conical shape or a columnar shape can also be used.
[0017]
By the way, even when fan-shaped fuel spraying requires a large amount of fuel at a high engine load, it becomes difficult in time to inject fuel only in the latter half of the compression stroke, and fuel is injected during the intake stroke. And homogeneous combustion is performed.
[0018]
In order to achieve good homogeneous combustion, a strong tumble flow is generated in the cylinder during the intake stroke, the injected fuel is sufficiently atomized by this tumble flow and stirred, and the mixture is sufficiently homogenized until ignition It is necessary to form a mind. Further, since the strong tumble flow causes turbulence in the cylinder at the time of ignition, the combustion speed in homogeneous combustion can be increased.
[0019]
As a result, in the present embodiment, the intake port 1 allows the required maximum amount of intake air at the time of engine high load to pass through, and the stronger the amount of intake air supplied into the cylinder, the stronger the tumble flow in the cylinder The overall shape and formation of the connection part in the cylinder are devised so as to generate FIG. 3 shows the latter half of the intake stroke, and the tumble flow generated in the cylinder descends on the exhaust valve side in the cylinder as shown by the arrow, and the intake valve in the cylinder passes through the top surface of the piston 5. It is an intake swirl flow that swirls in the cylinder in the vertical direction so as to rise upward. Thus, homogeneous combustion is performed in the first operation region A of high rotation or high load in FIG. 4, but a relatively large amount of intake air at this time can be sufficiently supplied into the cylinder via the intake port 1. At the same time, a relatively strong tumble flow is generated in the cylinder by a relatively large amount of intake air. As a result, a sufficiently homogenized homogeneous mixture is formed, and the combustion speed is increased by the turbulence in the cylinder at the time of ignition accompanied by a strong tumble flow, and good homogeneous combustion can be realized.
[0020]
On the other hand, stratified combustion is performed in the second operation region B of the low rotation / low / medium load and the third operation region C of the medium rotation / low / medium load in FIG. In the second operation region B, since the required intake air amount is small, the intake air amount is reduced to such an extent that the pumping loss does not increase so much by a throttle valve (not shown) arranged on the upstream side of the intake port 1. As a result, the amount of intake air supplied into the cylinder via the intake port 1 is reduced, and the tumble flow generated in the cylinder becomes weak. Such a weak tumble flow disappears by the second half of the compression stroke, which is the fuel injection timing during stratified combustion, so that the formation of the combustible mixture is inhibited or the formed combustible mixture is There is no such thing as dispersion. Thus, in the second operation region B, good stratified combustion can be realized.
[0021]
However, in the third operation region C, the required intake air amount is not so small, and the intake air amount can be reduced somewhat by the throttle valve, but the required intake air amount at this time is reduced in the cylinder via the intake port 1. , The tumble flow generated in the cylinder becomes relatively strong and does not disappear by the latter half of the compression stroke. Accordingly, in this state, the formation of the combustible mixture is inhibited by the tumble flow, or the formed combustible mixture is dispersed before the ignition, and good stratified combustion cannot be realized.
[0022]
In the present embodiment, in order to realize good stratified combustion in the third operation region C, the lift amount of the intake valve 3 in the intake stroke is made small as shown by a one-dot chain line in FIG. At this time, the throttle valve is fully opened, and the intake air amount supplied into the cylinder is reduced by the intake valve 3 so that the required intake air amount is supplied into the cylinder. For example, when the intake air amount is decreased by the throttle valve, the intake air flow velocity on the upstream side of the throttle valve becomes slow, but the intake air flow velocity on the downstream side of the throttle valve, that is, the intake air flow velocity in the intake port 1 is negative pressure in the cylinder. Will be relatively fast. On the other hand, when the intake air amount is decreased by the intake valve 3, the intake air flow velocity upstream of the intake valve 3, that is, the intake air flow velocity in the intake port 1 can be delayed.
[0023]
Thus, the intake air is directed so as to easily generate a tumble flow in the cylinder when passing through the intake port 1, but the intake air flow rate in the intake port 1 is slowed by reducing the intake air amount by the intake valve 3. In addition, the direction to intake air is weakened, and the tumble flow generated in the cylinder can be weakened. As a result, good stratified combustion can be realized in the third operation region C. In order to realize a desired intake amount for each operating state in the third operation region C, the lift amount variable mechanism that can change the lift amount of the intake valve 1 steplessly is used only by the intake valve 3. Although the intake amount may be controlled, in the case of a lift amount variable mechanism in which the lift amount of the intake valve 1 can be switched only in two stages, the lift amount of the small intake valve 3 is selected, and the desired intake amount is As realized, the opening degree control of the throttle valve may be combined.
[0024]
In the above-described embodiment, the intake valve 3 is used as the suppression means for suppressing the tumble flow, but in another embodiment shown in FIG. 5, the exhaust valve 4 is used as the suppression means. The closing timing of the exhaust valve 4 is generally just after intake top dead center in order to increase exhaust efficiency. However, if this closing timing is further retarded, exhaust gas is discharged from the exhaust port 2 at the beginning of the intake stroke. Flows back into the cylinder. In the present embodiment, in the third operation region C, the exhaust gas is caused to flow backward from the exhaust port 2 into the cylinder at the beginning of the intake stroke, or the exhaust gas flowing backward from the exhaust port 2 into the cylinder is increased. As shown, the intake air supplied from the intake port 1 into the cylinder collides with the backflow exhaust gas to weaken the inertial force of the intake and weaken the tumble flow generated. Thereby, good stratified combustion can be realized in the third operation region C.
[0025]
FIG. 6 shows still another embodiment of a direct injection spark ignition internal combustion engine according to the present invention. In the present embodiment, the intake port 1 ′ is different from the embodiment described so far, and as shown by an arrow in FIG. 6, the intake port 1 ′ descends on the intake side in the cylinder and passes through the top surface of the piston 5. A reverse tumble flow that swirls in the cylinder in the longitudinal direction is generated in the cylinder so as to rise on the exhaust valve side. Further, similarly to the embodiment shown in FIG. 5, the closing timing of the exhaust valve 4 is retarded so that the exhaust gas flows backward from the exhaust port 2 into the cylinder. This counter-flow exhaust gas tries to swivel in the vertical direction so as to descend the intake valve side in the cylinder and ascend the exhaust valve side, and as described above, it collides with the tumble flow, but it becomes a reverse tumble flow. On the other hand, it works to strengthen it.
[0026]
Thus, in the first operation region A, the reverse tumble flow generated by the intake air supplied from the intake port 1 ′ into the cylinder is strengthened by the exhaust gas flow that flows backward from the exhaust port 2 into the cylinder at the beginning of the intake stroke. A strong reverse tumble flow is generated in the cylinder. Of course, even with such a strong reverse tumble flow, the fuel injected in the intake stroke at the time of homogeneous combustion can be made into a homogeneous homogeneous mixture, and the turbulence in the cylinder at the time of ignition will be disturbed. Good homogeneous combustion can be realized in the operation region A.
[0027]
In the second operation region B, the amount of intake air required to pass through the intake port 1 ′ is small, and the reverse tumble flow generated by intake air becomes very weak. Thereby, even if the reverse tumble flow is strengthened by the reverse flow exhaust gas, the reverse tumble flow in the cylinder is weak and disappears in the latter half of the compression stroke, so that the stratified combustion is not deteriorated.
[0028]
However, in the third operation region C, the necessary intake amount passing through the intake port 1 ′ is relatively large, and as it is, if the reverse tumble flow generated in the cylinder is strengthened by the reverse flow exhaust gas, as a result, The reverse tumble flow in the cylinder becomes stronger and worsens stratified combustion. Accordingly, in the present embodiment, in the third operation region C, the valve closing timing of the exhaust valve 4 is advanced as the suppression means, the backflow exhaust gas amount is reduced, or the exhaust gas is prevented from backflowing, The reverse tumble flow generated in the cylinder is not strengthened. Thus, a strong reverse tumble flow that does not disappear even in the latter half of the compression stroke is not generated, and good stratified combustion can be realized.
[0029]
In the embodiments described so far, the intake swirl flow generated in the cylinder in order to achieve good homogeneous combustion is a tumble flow or a reverse tumble, but this does not limit the present invention, and the inside of the cylinder is not limited. It may be a swirl flow that turns around the axis. If a strong swirl flow is generated in the cylinder, the fuel injected in the intake stroke can be finely atomized and agitated as well as the strong tumble flow, and can also cause turbulence in the cylinder at the time of ignition. And homogeneous combustion can be improved. However, since the strong swirl flow does not disappear even in the latter half of the compression stroke, the stratified combustion is deteriorated by dispersing the combustible mixture before ignition in the stratified combustion.
[0030]
As a result, it is possible to pass the maximum amount of intake air required for homogeneous combustion at high engine load, and to increase the intake air amount supplied to the cylinder so that a stronger swirl flow is generated in the cylinder. Is formed, good homogeneous combustion can be realized in the first operation region A, and in the second operation region B where the required intake air amount is small, the swirl flow is weakened and good stratified combustion is realized. be able to. Further, in the third operation region C, if the intake amount is decreased by reducing the lift amount of the intake valve 3 in order to obtain the required intake amount, the swirl flow is weakened and good stratified combustion is realized. Can do. As a means for suppressing such swirl flow, the exhaust gas may be backflowed into the cylinder by retarding the closing timing of the exhaust valve, and the reverse flow exhaust gas does not swirl in the same direction as the swirl flow. It works to weaken the swirl flow by colliding with the swirl flow.
[0031]
By the way, the exhaust gas that has flowed back into the cylinder from the exhaust port lowers the combustion temperature and reduces the amount of NO _x produced, as with the recirculated exhaust gas. When a normal exhaust gas recirculation device is provided, the recirculation exhaust gas amount may be reduced in consideration of the backflow exhaust gas amount into the cylinder. Also, if an exhaust throttle valve is provided in the engine exhaust system, the exhaust pressure in the exhaust port at the beginning of the intake stroke is increased by restricting the engine exhaust system by this exhaust throttle valve, and the timing of closing the exhaust valve is increased. Even if it is the same, the backflow exhaust gas amount into the cylinder can be increased. Thereby, for example, when the required intake air amount is relatively large in the third operation region C and the intake air swirl flow becomes considerably strong, the exhaust valve closing timing is retarded and the engine exhaust system is throttled by the exhaust throttle valve. May be.
[0032]
In the above-described embodiment, in the second operation region B, the intake swirl flow generated in the cylinder is weak because the required intake air amount is small, and the intake swirl flow is not weakened by the suppression means. However, of course, at this time, the intake swirl flow may be further weakened by the suppressing means. Also in the second operation region B, when the throttle valve is fully opened to reduce the pumping loss and the intake amount similar to that in the third operation region C is supplied into the cylinder, the same as in the third operation region C. It is necessary to weaken the intake swirl flow by the suppression means.
[0033]
【The invention's effect】
Thus, according to the in-cylinder spark ignition internal combustion engine according to the present invention, the intake port allows the maximum amount of intake air required for homogeneous combustion at the time of high engine load to pass through and is supplied into the cylinder. The higher the intake air amount, the stronger the intake swirl flow is generated in the cylinder. Unlike the homogeneous combustion, the throttle valve is fully opened during stratified combustion, and the lift amount of the intake valve is reduced by the variable lift amount mechanism. As a result, the amount of intake air passing through the intake port is reduced as compared with the case of homogeneous combustion, and the intake swirl flow generated in the cylinder is weakened. As a result, during homogeneous combustion, a strong intake swirl flow can be reliably generated in the cylinder during the intake stroke without causing a shortage of intake air amount, and during stratified combustion, a strong intake swirl flow is the lift amount of the intake valve. Therefore, it is possible to prevent the generation of a strong intake swirl flow in the cylinder, so that both homogeneous combustion and stratified combustion can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention.
2 is a plan view of a piston of the direct injection spark ignition internal combustion engine of FIG. 1. FIG.
3 is a schematic longitudinal sectional view in an intake stroke of the direct injection spark ignition internal combustion engine of FIG. 1; FIG.
FIG. 4 is a map for switching between homogeneous combustion and stratified combustion.
FIG. 5 is a schematic longitudinal sectional view showing another embodiment of a direct injection spark ignition internal combustion engine according to the present invention.
FIG. 6 is a schematic sectional view showing still another embodiment of the direct injection spark ignition internal combustion engine according to the present invention.
[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

Claims (1)

An in-cylinder injection spark ignition internal combustion engine having an ignition plug, a variable lift amount of an intake valve, and a fuel injection valve for directly injecting fuel into a cylinder and switching between stratified combustion and homogeneous combustion The intake port allows the maximum amount of intake air required for the homogeneous combustion at the time of high engine load to pass, and generates a stronger intake swirl flow in the cylinder as the amount of intake air supplied to the cylinder increases. In the stratified combustion , unlike the homogeneous combustion, the throttle valve is fully opened, and the lift amount of the intake valve is reduced by the variable lift amount mechanism, so that the intake air is compared with the homogeneous combustion. An in-cylinder injection spark ignition internal combustion engine characterized in that the amount of intake air passing through a port is reduced to weaken the intake swirl flow generated in the cylinder.

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