JP2003269220A - Structure and control device of low exhaust emission cylinder injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such problems with a cylinder injection engine basically performing stoichiometric combustion as a combustion configuration where the assurance of the stability of combustion is difficult to be compatible with the suppression of smoke when a large amount of exhaust gas is recirculated by a conventional engine configuration and control method, and the fuel economy is not improved. <P>SOLUTION: This control device comprises a tumble generating means and a piston capable of holding tumbles formed in a combustion chamber to the latter half of a compression stroke by the tumble generating means. Fuel injection is desirably performed two times in an intake stroke and a compression stroke. In an exhaust recirculation area, the timing of a latter injection injected in the compression stroke or an injection rate is controlled according to the operating state of the engine. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-cylinder injection engine based on stoichiometric combustion as a combustion mode, in which a large amount of exhaust gas is recirculated to improve fuel efficiency in a predetermined operating range.
The present invention relates to a configuration and a control device of a cylinder injection engine that can suppress deterioration of combustion and generation of smoke even when a large amount of exhaust gas is recirculated.

[0002]

2. Description of the Related Art In recent years, in-cylinder injection engines for directly supplying fuel into cylinders have been rapidly developed in order to achieve both improvement of fuel consumption and securing of output. Thus, a type of switching between stratified lean combustion and homogeneous stoichiometric combustion has been put into practical use. Traditionally,
As a control device and control method for this type of direct injection engine, for example, in Japanese Patent Application Laid-Open No. 7-119507, an engine is operated in a stratified combustion state in a low load region, while it is operated in a uniform combustion state in a high load region. When the engine is operating at low speed and in the high load range, the fuel is injected from the fuel injection valve by dividing the fuel into two in the intake stroke of the cylinder, so that half of the early injected fuel is used in the intake stroke. While the fuel is diffused in the combustion chamber by the end, the remaining half of the fuel injected in the latter period is diffused in the combustion chamber of the increased volume and all the fuel is injected all at once. It has been proposed to prevent the formation of a rich air-fuel mixture in the vicinity of the surface and prevent the generation of smoke.

Further, in Japanese Patent Laid-Open No. 11-218050, in the operating region where the engine is in a uniform combustion state and in a rich state, the central timing between the early injection timing and the late injection timing of the fuel is taken from the fuel injection valve in the intake stroke. The fuel is injected in two splits so that it is earlier than the center of the stroke, and a large amount of exhaust gas is recirculated to the intake passage by the exhaust gas recirculation device.
It is disclosed that the generation of Ox is suppressed and the concentration ratio of the HC concentration to the NOx concentration in the exhaust gas (HC / NOx) is increased to promote refreshment of the catalyst.

[0004]

In a cylinder injection engine of the type in which the combustion mode is switched between stratified lean combustion and homogeneous stoichiometric combustion according to the operating state of the engine, when stratified lean combustion is performed under predetermined operating conditions. Since a large amount of NOx is generated, in addition to a three-way catalyst as an exhaust structure, a catalyst dedicated to NOx adsorption is indispensable, and an increase in system cost is unavoidable. From the viewpoint of complying with strict exhaust gas regulations to be introduced in the future and reducing system costs, it is necessary to significantly increase the ratio of stoichiometric combustion in the prescribed operating state where conventional stratified lean combustion was performed. However, reducing the stratified lean combustion operation region leads to a reduction in the fuel consumption improving effect, which is one of the features of in-cylinder injection. As one of fuel consumption improving means, there is a method of recirculating a large amount of exhaust gas. In a cylinder injection engine that is currently in practical use, during stratified lean combustion, the fuel injected in the compression stroke collides with the piston wall surface and is conveyed toward the ignition plug, and the combustible mixture is ignited around the ignition plug at the ignition timing. Is formed. In this way, when a required amount of fuel is collectively injected in the first half of the intake stroke in a cylinder injection engine in which fuel is guided by the piston wall surface, a uniform air-fuel mixture is formed in the combustion chamber at the ignition timing, but is recirculated. A small amount of exhaust hinders flame propagation. Therefore, a sufficient effect of improving fuel economy cannot be obtained. On the other hand, when the fuel required for the compression stroke immediately before ignition is collectively injected, a stratified air-fuel mixture is formed in the combustion chamber at the ignition timing, so that more exhaust gas is exhausted than in the case of the uniform air-fuel mixture formation. However, a large amount of smoke is generated due to excessive concentration of fuel around the spark plug or adhesion of fuel to the piston wall. Further, when the fuel injection timing is set to an intermediate timing between the first half of the intake stroke and the compression stroke immediately before ignition, the exhaust gas cannot be sufficiently recirculated and at the same time smoke is generated. In the above engine configuration, it is extremely difficult to ensure both combustion stability and smoke suppression while recirculating a large amount of exhaust gas.

[0005]

[Means for Solving the Problems] To achieve the above object,
The structure and control method of the in-cylinder injection engine of the present invention is essentially a high load region in which the throttle valve for controlling the air amount is in the vicinity of full opening, an operating region above a predetermined engine speed, and a low operating condition including idle operation. In any operating state except the load region, in any operating state, the tumble generating means forms a tumble flow in the combustion chamber and recirculates the exhaust gas into the combustion chamber, so that the mixing ratio of fresh air and fuel becomes near stoichiometry. In this manner, the fresh air amount and the fuel injection amount are controlled, and all or part of the fuel injected from the fuel injection valve during one cycle is injected in the intake stroke.

In the above aspect, preferably, the tumble generating means is composed of a two-stage intake port in which the intake port is divided into upper and lower parts, and a valve capable of opening and closing only the lower part of the intake port on the upstream side thereof. Is.

In the above aspect, preferably, the stratified lean combustion is performed only in the low load region including the idle operation.

In the above aspect, it is preferable that the engine has an idle stop control means for stopping the engine only when the vehicle is completely stopped.

In the above-mentioned aspect, it is preferable that an operating region excluding a high load region in which a throttle valve for controlling the air amount is in the vicinity of full opening, an operating region at a predetermined engine speed or more, and a low load region including idle operation. In the above, the fuel injection is divided into two parts, the intake stroke and the compression stroke.

In the above aspect, preferably, when the injection ratio of the early injection injected in the intake stroke and the late injection injected in the compression stroke and the early injection timing are constant, the late injection timing is changed according to the operating condition. Is.

In the above aspect, preferably, the injection timings of the early injection injected in the intake stroke and the late injection injected in the compression stroke are both fixed, and the injection ratio of the early injection and the late injection is changed according to the operating state. This is the case.

Even during stoichiometric combustion, a large amount of exhaust gas recirculation is possible, and not only exhaust gas reduction but also fuel efficiency improvement can be achieved at the same time.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an in-cylinder injection engine system of the present invention. In the engine, a fuel injection valve 2 is provided on a side surface of a combustion chamber 1 and an ignition plug 3 is arranged at a central portion of an upper surface of the combustion chamber 1, and an intake valve is provided. Fuel can be injected into the combustion chamber 1 at any time regardless of the operation of No. 4.

As for the structure of the intake system, a tumble generating mechanism 6 is arranged in the intake port 5 immediately before the combustion chamber in order to form a vertical air flow, that is, tumble, in the combustion chamber 1. The crown shape of the piston 7 is a concave shape capable of holding the tumble until the latter half of the compression stroke. Further, in order to recirculate a part of exhaust gas to the combustion chamber again in a predetermined operating state, an exhaust port 9 upstream of the catalyst 8 and a collector 11 arranged downstream of a throttle valve 10 for adjusting the amount of air are provided. An exhaust gas recirculation passage 13 to be connected is provided, and by adjusting the electromagnetic valve 12 in the middle of the exhaust gas recirculation passage 13, optimum exhaust gas can be recirculated according to the operating state. On the other hand, this system simplifies the exhaust structure and improves the efficiency of exhaust gas by switching the conventional homogeneous stoichiometric combustion and stratified lean combustion to control the stratified lean combustion region of the direct injection engine. Can be purified. The catalyst 8 is a three-way catalyst.

Further, many signals such as a crank angle sensor signal and an air flow sensor 27 signal for measuring the intake air amount are input to the ECU 14, and the engine is controlled according to the operating conditions.

Next, each operating region and exhaust gas recirculation region set in the cylinder injection engine of the present invention will be described with reference to FIGS. 2 and 3.

In a high load region where the throttle valve is almost fully opened and a region where the load is high at a predetermined rotation speed or higher and a relatively high load, a mixture richer than stoichiometric and uniform is formed and burned. On the other hand, the operating region excluding the operating region and a region under a predetermined load is basically near stoichiometric and forms a stratified air-fuel mixture for combustion, and exhausts the entire region as shown in FIG. By recirculating the exhaust gas, the exhaust gas is efficiently purified with a catalyst and the fuel consumption is improved. Furthermore, in the operating range lower than the prescribed load, that is, in the low load range including idle operation, even if a uniform air-fuel mixture is formed and burned in the vicinity of stoichiometry depending on the aim of the system, or the air-fuel mixture is positively stratified. It may be burned at a lean air-fuel ratio. Further, in the idle operation state, when the vehicle is completely stopped, the engine may be temporarily stopped by the idle stop control.

Next, FIG. 4 is a perspective sectional view of a preferred cylinder injection engine to which the present invention is applied.

The tumble generating mechanism shown in FIG. 1 has a partition plate 15 and a partition plate 15 which divide the intake port 5 into upper and lower parts.
And a tumble intensity control valve 16 disposed upstream of The means for forming the tumble in the combustion chamber is shown in FIG. As described above, the intake port 5 is divided into the upper and lower two stages by the partition plate, and the tumble strength control valve 16 is provided upstream thereof.
In addition to the configuration (a) in which the elements are arranged, configurations (b), (c), etc. are possible.

For example, as shown in (b), the structure of only the tumble intensity control valve 16 in (a) can be considered. The tumble strength is the upper half of the intake valve 4 (spark plug 3
When the ratio of air taken in from (side) is large, it becomes strong, and conversely, when it is small, it becomes weak. The angle θP of the intake port 5 varies depending on the engine, but the tumble strength (basic strength in the state without the tumble generating means) also varies depending on the θP. Therefore, if the required tumble strength can be obtained with the simplified intake system configuration, the simplified configuration as shown in (b) can be said to be effective from the viewpoint of cost reduction.

As a means for strengthening the tumble by devising the intake valve ((c) in the figure), an intake suppressing member 17 is formed so that it is difficult for air to enter the lower side of the intake valve 4 (fuel injection valve 2 side). There are possible ways to do this. In the region where the lift amount of the intake valve is small, the intake suppressing member 1
Most of the intake air passes through the upper half of the intake valve 4 by 7 and is sucked into the combustion chamber. The larger the lift amount, the smaller the effect, but a sufficient effect can be obtained as compared with the case where the suction suppression member 17 is not provided. However, the degree of freedom in controlling the tumble strength is lower than that in (a) and (b).

By the tumble generating means as described above, the air sucked in during the intake stroke forms a tumble in the combustion chamber 1. A groove for storing the tumble is formed on the crown surface of the piston 7. FIG. 6 shows an example of the shape of the piston crown surface. As can be seen from the vertical cross section of the piston shown in the lower part of the figure, the grooves are formed so that the intake side and the exhaust side are symmetrical. As a groove shape when the piston is viewed from above, a shape that is symmetrical in the vertical direction in the figure with respect to a straight line passing through the center of the piston and connecting the intake side and the exhaust side is desirable.
In the case of a rectangle as in (a), in the case of a trapezoid where the width of the groove is continuously narrowed from the exhaust side to the intake side as in (b), or in the elliptical shape as in (c). May be.

Next, the exhaust gas recirculation rate and the surge torque by the in-cylinder injection engine having the above-described tumble generating means and the piston capable of storing the tumble until the latter half of the compression stroke,
Alternatively, the relationship between the exhaust gas recirculation rate and fuel consumption will be described. The graph shows the result when the required fuel is collectively injected in the intake stroke.

FIG. 7 shows the relationship between the exhaust gas recirculation rate and the surge torque which is an index of combustion stability. When the tumble strength control valve of the present invention is fully opened, combustion is stable even when a large amount of exhaust gas is recirculated, as compared to the conventional wall guide method that employs a swirl (lateral air flow), as shown in FIG. As you can see, fuel efficiency is improving. Further, when the tumble strength control valve is fully closed, combustion is stable even in a state where the exhaust gas recirculation rate is twice or more that in the conventional case, and fuel efficiency is improved. The reason why combustion is stable even when a large amount of exhaust gas is recirculated by the engine configuration of the present invention will be described with reference to FIG.

Although there are strengths and weaknesses in the intake stroke, the combustion chamber 1
A tumble is formed inside. However, since the air is sucked from the two intake valves 4, the strong tumble flow 18a, 18a,
18b has occurred. Also, the piston 7 holds the tumble flows 18a and 18b until the latter half of the compression stroke. The fuel injection position injected in the intake stroke is between the tumble flows 18a and 18b, and the fuel spray 19 injected from the fuel injection valve 2 is the tumble flow 18a.
And 18b play the role of an air curtain, and the lateral diffusion of the combustion chamber 1 becomes difficult until the latter half of the compression stroke. Therefore, even if the fuel is injected in the intake stroke, a combustible mixture richer than in the conventional case is formed around the spark plug 3, so that stable combustion can be obtained against exhaust gas recirculation.

Next, with reference to FIGS. 10 to 12, an example of a fuel spray shape suitable for the present invention will be described.

First, the spray shown in FIG. 10 has a spray shape having the characteristics shown in FIGS. As can be seen from the vertical cross section of the spray shown in the upper part of the drawing and the horizontal cross section of the lower part of the drawing, the spray is symmetrical vertically and horizontally with respect to the center line of the fuel injection valve. On the other hand, examples of preferable spray shapes for the present invention include those shown in FIGS. 11 and 12.

As shown in FIG. 10, the shape of the fuel spray sprayed from the fuel injection valve is not symmetrical. This can be formed by making the direction of the nozzle flow path of the fuel injection valve have a specific angle with respect to the center line direction of the fuel injection valve. In the fuel spray formed by such a nozzle structure, the penetration in the angled direction becomes longer and the flow rate distribution also increases. When such spray is applied, the fuel injection center line is arranged so as to be inclined toward the spark plug side with respect to the center line of the fuel injection valve. By doing so, it is easy to convey the fuel toward the spark plug, and the vaporized fuel is likely to collect around the spark plug.

The spray shape shown in FIG. 11 is a flat shape and can be formed, for example, by forming the nozzle tip into a slit shape. When such spraying is applied, as shown in the cross section, the side where the distance from the center line of the fuel injection valve is long is the spark plug side and the piston side. By doing so, diffusion of fuel in the lateral direction of the fuel chamber is prevented, and a rich combustible mixture is formed around the spark plug.

By applying the above-mentioned spray, the stratified air-fuel mixture can be formed in the combustion chamber even during the intake stroke injection, so that a large amount of exhaust gas recirculation can be achieved even during stoichiometric combustion, and fuel efficiency can be improved.

In order to enable a large amount of exhaust gas recirculation by stoichiometric combustion, it is important to prevent the fuel from adhering to the piston wall surface and stratify the air-fuel mixture without excessively concentrating the vaporized fuel around the spark plug. . Next, the means realized by the fuel injection control will be described.

FIG. 13 shows a fuel injection control method that enables a large amount of exhaust gas recirculation. For example, in the control method 1, the fuel injection is divided into two parts, that is, the intake stroke and the compression stroke, and the injection ratio and the early injection timing of the first half injection that is injected in the intake stroke and the second half injection that is injected in the compression stroke are constant. This is a method of changing the injection timing according to the operating state. This control method is based on the fact that the concentration of combustible mixture around the spark plug changes when the latter injection timing is changed as shown in FIG. An example different from the control method 1 will be described as the control method 2. Similar to the control method 1, the fuel injection is performed by dividing into the intake stroke and the compression stroke, but the control method 2
This is a system in which the injection timings of the early injection injected in the intake stroke and the late injection injected in the compression stroke are both constant, and the injection ratio of the early injection and the late injection is changed according to the operating state. Basically, when a predetermined engine load is required, a certain amount of fuel is required. For example, if it is desirable to increase the fuel injection amount in the first period, reduce the fuel injection amount in the second period. Control. This control method is shown in FIG.
This is a method that utilizes the fact that the concentration of the combustible mixture around the spark plug changes when the ratio of the fuel injection amount in the previous period to the fuel injection amount in the latter period, that is, the injection ratio, is changed as shown in FIG. Furthermore, the control system becomes a little complicated, but control method 1 and control method 2
The same effect can be obtained by a combination of the above.

As shown in FIG. 16, the mixture distribution when the fuel injection control is applied, as shown in FIG. 16, the early injection fuel injected in the intake stroke is the late injection regardless of which fuel injection control is adopted. At the start time, it diffuses in the combustion chamber, and by forming a rich combustible air-fuel mixture around the spark plug with the late injection fuel, an optimal stratified air-fuel mixture can be realized during stoichiometric combustion.

According to the present invention, it is possible to ensure both the stability of combustion and the suppression of smoke when a large amount of exhaust gas recirculates.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a cylinder injection engine system of the present invention.

FIG. 2 is a diagram showing each operating region set in the direct injection engine of the present invention.

FIG. 3 is an exhaust gas recirculation region set in the in-cylinder injection engine of the present invention.

FIG. 4 is a perspective sectional view of a preferred cylinder injection engine to which the present invention is applied.

FIG. 5: Means for forming tumble in a combustion chamber.

FIG. 6 shows an example of a piston crown surface shape.

FIG. 7 shows the relationship between the exhaust gas recirculation rate and the surge torque in the direct injection engine of the present invention.

FIG. 8 shows a relationship between exhaust gas recirculation rate and fuel consumption in the direct injection engine of the present invention.

FIG. 9 shows mixture formation during intake stroke injection in the cylinder injection engine of the present invention.

FIG. 10 is a spray shape applied in FIGS. 7 and 8.

FIG. 11 is a preferable spray shape in the cylinder injection engine of the present invention.

FIG. 12 is a preferable spray shape in the cylinder injection engine of the present invention.

FIG. 13 is a fuel injection control method that enables a large amount of exhaust gas recirculation.

FIG. 14 shows the relationship between the late injection timing and the combustible mixture concentration around the spark plug when the injection ratio is constant.

FIG. 15 shows the relationship between the ratio of the early injection and the late injection when the injection timing is constant and the combustible mixture concentration around the spark plug.

FIG. 16 is an air-fuel mixture distribution when the fuel injection control is applied.

[Explanation of symbols]

1 ... Combustion chamber, 2 ... Fuel injection valve, 3 ... Spark plug, 4
... intake valve, 5 ... intake port, 6 ... tumble generating mechanism, 7 ... piston, 8 ... catalyst, 9 ... exhaust port, 10 ...
Throttle valve, 11 ... Collector, 12 ... Electromagnetic valve, 13 ... Exhaust gas recirculation passage, 14 ... ECU, 15 ... Partition plate, 16 ... Tumble strength control valve, 17 ... Intake suppressing member, 18a, 18b ... Tumble flow, 19 ... Fuel Spray,
20 ... Early injection fuel, 21 ... Late injection fuel.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02B 31/00 301 F02B 31/00 301B 3G301 F02D 17/00 F02D 17/00 Q 21/08 301 21/08 301C 29/02 321 29/02 321A 41/02 325 41/02 325E 325G 41/34 41/34 H 43/00 301 43/00 301J 301N 301U 45/00 312 45/00 312J F02M 25/07 550 F02M 25 / 07 550G 550R 570 570A F term (reference) 3G023 AA02 AA05 AB03 AC05 AD06 AD29 AG01 AG03 3G062 AA07 AA08 BA02 CA03 CA07 CA08 EA12 GA05 GA06 GA16 GA17 3G084 FA03 FA10 FA10 FA33 FA10 FA03 FA10 CA03 FA04 CA07 CA07 CA10 FA07 CA02 CA10 FA07 AA09 AA10 AA17 BB06 BB12 BB13 DC06 DC09 DE03S EA07 EA08 FA15 FA24 FA30 GA04 GA06 GB10 HA01Z HA08Z HE01Z HE03Z 3G093 BA19 BA20 BA21 BA22 CA04 CA07 DA06 DA07 DA09 EA10 FA11 3G301 HA04 HA13 HA16 HA17 JA02 JA26 KA07 KA09 KA28 LA05 LB04 MA19 MA26 MA27 NA08 NE15 PA01Z PA13Z PE01Z PE03Z

Claims (7)

[Claims] 1. A fuel injection valve for directly injecting fuel into a cylinder, a tumble generating means in an intake system, and a concave piston for holding a tumble formed in the combustion chamber by the tumble generating means until the latter half of a compression stroke. And an exhaust gas recirculation passage for recirculating a part of the exhaust gas from the exhaust pipe to the intake pipe,
In a spark ignition in-cylinder injection engine equipped with an exhaust gas recirculation amount control valve for controlling the amount of exhaust gas recirculated to the exhaust gas recirculation passage, a throttle valve for controlling the air amount and a predetermined high load region in which the throttle valve is in the vicinity of full opening are provided. In an operating range excluding an operating range equal to or higher than the engine speed and a low load range including idle operation, the tumble generating means forms a tumble flow in the combustion chamber and recirculates exhaust gas to the combustion chamber in any operating state. However, the fresh air amount and the fuel injection amount are controlled so that the mixing ratio of the fresh air and the fuel is close to stoichiometric, and all or part of the fuel injected from the fuel injection valve in one cycle is in the intake stroke. An in-cylinder injection engine system characterized by injecting into a cylinder. 2. The in-cylinder injection engine system according to claim 1, wherein the intake port is a vertically divided two-stage intake port, and the upstream side thereof has a valve capable of opening and closing only the lower stage of the intake port. 3. The in-cylinder injection engine system according to claim 1, wherein stratified lean combustion is performed only in a low load region including idle operation. 4. The cylinder injection engine system according to claim 1, further comprising an idle stop control means for stopping the engine only when the vehicle is completely stopped. 5. An intake stroke is set in an operating range excluding a high load range in which a throttle valve for controlling the air amount is in the vicinity of full opening, an operating range at or above a predetermined engine speed, and a low load range including idle operation. 2. The in-cylinder injection engine system according to claim 1, wherein the fuel is injected in two divided compression strokes. 6. The injection ratio of the early injection injected into the intake stroke and the late injection injected into the compression stroke, and the early injection timing are kept constant, and the late injection timing is changed according to the operating condition. 5 In-cylinder injection engine system. 7. The injection timing of the early injection injected during the intake stroke and the injection timing of the late injection injected during the compression stroke are both constant,
The in-cylinder injection engine system according to claim 5, wherein the injection ratio of the first-stage injection and the second-stage injection is changed according to the operating state.