JPH10212986A - In-cylinder injection type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the exhausting rate of HC and the like, and improve emission by suppress to stick fuel on a cylinder head when at least a part of injection fuel is injected in an intake stroke, in an in-cylinder injection type engine. SOLUTION: In an in-cylinder injection type engine, an ignition plug 10 is arranged on nearly center part of a combustion chamber 5, an injector 11 is arranged on a circumferential rim part of the combustion chamber 5 so as to inject fuel downward slantly, and a recessed shaped cavity 13 is arranged on a top part of a piston 4. In the case of injection in a compression stroke, an injection direction is faced into the cavity 13, and fuel reflected by the cavity 13 attains near the ignition plug 10. On the other hand, in the case of injection in a suction stroke, an injection direction is slid from the cavity 13, and an injection start timing of injection in the suction stroke is set within 70 deg.±20 deg. after top dead point by a crank angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection engine having an injector for directly injecting fuel into a combustion chamber.

[0002]

2. Description of the Related Art Conventionally, an injector for directly injecting fuel into a combustion chamber is provided, and when the load is low, the fuel is injected from the injector at a later stage of the compression stroke, so that the mixture is unevenly distributed around the ignition plug. 2. Description of the Related Art There is known an in-cylinder injection engine in which the air-fuel ratio is made lean to improve fuel efficiency while ensuring combustion stability by performing stratified combustion.

In this in-cylinder injection engine, stratified combustion is performed when fuel is injected in the compression stroke as described above, while fuel is diffused and uniform combustion is performed when fuel is injected in the intake stroke. Therefore, the compression stroke injection and the intake stroke injection are selectively performed in accordance with the operation state, and the split injection for injecting the fuel in each of the intake stroke and the compression stroke is performed depending on the operation state.

For example, in a direct injection engine disclosed in Japanese Patent Application Laid-Open No. 8-193536, split injection is performed at the time of starting the engine (during cranking). In some cases, the intake stroke injection is performed when the engine is cold.

[0005]

As described above, in the direct injection engine, the fuel injection state is switched to the compression stroke injection, the intake stroke injection, the split injection, and the like according to the operation state. In such an engine, during the intake stroke injection during the intake stroke injection or the split injection, the injected fuel is diffused into the combustion chamber, but a part of the fuel may adhere to the cylinder wall. And, since the fuel adhering to the cylinder wall is difficult to burn, the larger the amount of fuel adhering to the cylinder wall, the more H
C emissions increase and emissions worsen. In particular,
When the engine is cold, the amount of HC emission tends to increase, and the adhesion of fuel to the cylinder wall poses a problem.

The present invention has been made in view of the above circumstances, and in a direct injection engine, when at least a part of the injected fuel is injected in an intake stroke, the fuel adhesion to a cylinder wall is suppressed to reduce HC and the like. It is an object of the present invention to provide an in-cylinder injection engine capable of reducing emissions of fuel and greatly improving emissions.

[0007]

The invention according to claim 1 is
In-cylinder injection in which an ignition plug is arranged at a substantially central portion of a combustion chamber formed above a piston in a cylinder bore, and an injector is arranged at a peripheral portion of the combustion chamber so as to inject fuel obliquely downward. A fuel injection control means for controlling at least a part of the injected fuel from the injector in the intake stroke in a specific operation state of the engine in the specific operation state of the engine is provided, and the injection start timing of the fuel injection in the intake stroke is set. 70 after top dead center at crank angle
It is set within the range of ± 20 °.

[0008] According to this configuration, the adhesion of the injected fuel to the cylinder wall due to the intake stroke injection can be reduced. In other words, when fuel is injected while the piston is very close to the top dead center, much of the fuel reflected at the top of the piston adheres to the cylinder wall, and fuel is injected when the piston is far away from the top dead center. When this occurs, the amount of fuel that reaches the cylinder wall directly and adheres increases, but at about 70 ° after the top dead center at the crank angle, the reflection of the injected fuel at the top of the piston decreases, and the injected fuel decreases as the piston descends. By being drawn downward, the fuel adheres to the cylinder wall less while the fuel is diffused appropriately.

As a result, the emission of HC (and CO) is reduced, and the emission is improved.

According to a second aspect of the present invention, in the engine according to the first aspect of the present invention, in a specific operation state of the engine, split injection is performed in which fuel is injected from the injector into an intake stroke and a compression stroke, respectively. It is.

With this arrangement, when the divided injection is performed, a relatively rich air-fuel mixture is formed in the area near the ignition plug by the compression stroke injection, and the mixture is formed around the area near the ignition plug by the intake stroke injection. A relatively lean air-fuel mixture is formed, and such an air-fuel mixture distribution state is advantageous for reducing HC and NOx as described later in the embodiment. By setting the timing of the intake stroke injection in this case as described above, fuel adhesion to the cylinder wall is reduced, and the effect of reducing HC and the like is enhanced.

According to a third aspect of the present invention, in the engine according to the second aspect, a concave cavity is provided at the top of the piston, and in the compression stroke injection, the injection direction is directed into the cavity and reflected by the cavity. In the intake stroke injection, the injection direction is set so as to deviate from the cavity while the fuel reaches the vicinity of the ignition plug.

[0013] In this case, the fuel from the compression stroke injection forms a relatively rich mixture near the spark plug,
The fuel from the intake stroke injection diffuses to form a uniform mixture, and a favorable mixture distribution state is obtained.

According to a fourth aspect of the present invention, in the engine according to the third aspect, the crank angle (θ1) between the intake top dead center and the injection start timing of the intake stroke injection, and the injection start timing of the compression stroke injection are set. Angle (θ2) between the angle and the compression top dead center
Is set so that θ1 ≧ θ2.

[0015] In this manner, the above-mentioned mixture distribution state can be obtained favorably.

According to a fifth aspect of the present invention, in the engine according to any one of the first to fourth aspects, a swirl generating means for generating a swirl in the combustion chamber is provided, and the fuel injected from the injector by the fuel injection control means. The swirl generating means is operated when at least a part of the swirl is controlled to be injected in the intake stroke.

According to a sixth aspect of the present invention, in the engine according to any one of the first to fourth aspects, a tumble generating means for generating a tumble in a combustion chamber is provided, and fuel injected from the injector by the fuel injection control means. Is controlled to inject at least a portion of the tumble during the intake stroke.

When the swirl or the tumble is formed as described above, the combustibility of the fuel injected in the intake stroke is improved, and the effect of reducing HC and the like is enhanced.

According to a seventh aspect of the present invention, a spark plug is disposed at a substantially central portion of a combustion chamber formed above a piston in a cylinder bore, and an injector is disposed obliquely downward at a peripheral portion of the combustion chamber. In a direct injection type engine arranged to inject fuel, fuel injection control means for controlling split injection of injecting fuel from the injector into an intake stroke and a compression stroke, respectively, in a specific operating state of the engine. In addition, a concave cavity is provided at the top of the piston so that the injection direction is directed toward the inside of the cavity during the compression stroke injection so that the fuel reflected by the cavity reaches the vicinity of the spark plug, while the injection during the intake stroke injection is performed. The direction is set so as to deviate from the cavity.

[0020] According to an eighth aspect of the present invention, a spark plug is disposed at a substantially central portion of a combustion chamber formed above a piston in a cylinder bore, and an injector is obliquely directed downward at a peripheral portion of the combustion chamber. In a direct injection engine arranged to inject fuel, fuel injection control means is provided for controlling split injection of injecting fuel into the intake stroke and the compression stroke from the injector in a specific operating state of the engine. At the same time, a concave cavity is provided at the top of the piston so that the fuel injected by the compression stroke injection is reflected by the cavity to reach the vicinity of the ignition plug, and the top dead center of the intake stroke and the injection start timing of the intake stroke injection are defined. And the crank angle (θ1) between the injection start timing of the compression stroke injection and the compression top dead center.
2) is set so that θ1 ≧ θ2.

According to the seventh and eighth aspects of the present invention, when split injection is performed, a relatively rich air-fuel mixture is formed in an area near the spark plug and a relatively lean air-fuel mixture is formed around the mixture. An air-fuel mixture distribution state in which air is formed is favorably obtained.

[0022]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a structure of a combustion chamber portion of a direct injection engine. In this figure, reference numeral 1 denotes an engine body, which comprises a cylinder block 2, a cylinder head 3, and the like, is provided with a plurality of cylinders, and a piston 4 is inserted into each of the cylinders.
A combustion chamber 5 is formed between the top surface of the cylinder head 3 and the lower surface of the cylinder head 3. An intake port 6 and an exhaust port 7, an intake valve 8 and an exhaust valve 9 for opening and closing these ports 6, 7, and a spark plug 10 are arranged in the combustion chamber 5. An injector 11 for directly injecting fuel is provided.

These structures will be specifically described. A lower surface of the cylinder head 3 is provided with a recess having a predetermined shape that forms the combustion chamber 5. The combustion chamber 5 is formed by, for example, a recess having a substantially trapezoidal cross section as illustrated. An intake port 6 is opened at an upper end surface of the combustion chamber 5, and an exhaust port 7 is opened at an inclined surface. The intake port 6 and the exhaust port 7 are shown one by one in the drawing, but are preferably provided two by two in a direction orthogonal to the paper surface. An intake valve 8 and an exhaust valve 9 are provided in each of the intake port 6 and the exhaust port 7, respectively. The intake valve 8 and the exhaust valve 9 are driven by a valve operating device (not shown) to open and close at a predetermined timing. It has become.

The ignition plug 10 is located at a substantially central portion of the combustion chamber 5 and is attached to the cylinder head 3 with an ignition gap facing the inside of the combustion chamber 5.

The injector 11 is provided in the combustion chamber 5
Is provided on the periphery. In the embodiment shown in FIG. 1, the injector 11 is attached to the cylinder head 3 at a side portion of the combustion chamber 5 on the side of the intake port 6, and the upper surface of the combustion chamber where the intake port 6 opens and the mating surface with the cylinder block 2. Injector 1 on the wall 12 between
The front end of the fuel cell 1 faces and injects fuel obliquely downward.

On the other hand, a concave cavity 13 is formed at the top of the piston 4 constituting the lower surface of the combustion chamber 5. The fuel is injected from the injector 11 toward the cavity 13 in the latter half of the compression stroke when the piston 4 is at a position close to the top dead center, and is further reflected by the cavity 13 so as to reach the vicinity of the spark plug 10. The relationship between the position and direction, the position of the cavity 13, and the position of the spark plug 10 is set in advance.

FIG. 2 schematically shows the entire engine including the intake / exhaust system.
Are connected to an intake passage 15 and an exhaust passage 16.
The downstream side of the intake passage 15 branches in the intake manifold for each cylinder, and two passages (only one passage is shown in the drawing) are formed in parallel in the cylinder-specific passage 15a, and two downstream end portions thereof are formed. The intake port 7 opens to the combustion chamber 5 shown in FIG. 1, and an intake flow control valve 17 is provided in one passage. And, the intake flow control valve 17
Is closed, swirl is generated in the combustion chamber 5 by the intake air introduced into the combustion chamber 5 from the other passage. Thus, the swirl generating means is constituted by the intake flow control valve 17 and the like.

A throttle valve 18 is provided in the middle of the intake passage 15, and the throttle valve 18 is operated by an electric actuator 19 such as a step motor so that the amount of intake air can be controlled. ing.

On the other hand, an O ₂ sensor 21 for detecting an air-fuel ratio in exhaust gas is provided in the exhaust passage 16 and a catalyst device 22 having a catalyst for purifying exhaust gas is provided. This catalyst device 22 may be constituted by a three-way catalyst, but in order to improve the purification performance in the case where the air-fuel ratio is made lean after warm-up and the stratified combustion is performed as described later, the catalyst device 22 is made leaner than the stoichiometric air-fuel ratio. It is desirable to use a catalyst having a function of purifying NOx even at a low air-fuel ratio. That is,
As is generally known, according to the three-way catalyst, HC, C
Although high purification performance for both O and NOx is limited to the vicinity of the stoichiometric air-fuel ratio, recently, in addition to the function of the three-way catalyst, a function of purifying NOx even at an air-fuel ratio leaner than the stoichiometric air-fuel ratio has been developed. Since a catalyst having a catalyst has been developed, it is preferable to use the catalyst to reduce NOx during lean operation.

When the catalyst device 22 is located in the exhaust passage 16 immediately downstream of the exhaust manifold 16a (directly connected to the exhaust manifold), the catalyst temperature tends to move movably at high speed and high load. A catalyst device 22 is provided in the middle of an exhaust pipe 16b connected to the exhaust manifold 16a so as to keep away from the engine.

Between the exhaust passage 16 and the intake passage 15,
An EGR passage 23 for returning a part of the exhaust gas to the intake system is connected, and an EGR valve 24 is provided in the EGR passage 23.

An ECU (control unit) 30 controls the engine. The ECU 30 includes a crank angle sensor 23 for detecting the crank angle of the engine,
An accelerator sensor 24 for detecting an accelerator opening (accelerator pedal depression amount), an air flow meter 25 for detecting an intake air amount, a signal from the water temperature sensor 26 and the O ₂ sensor 21 for detecting the water temperature of the engine cooling water or the like is input ing.

The ECU 30 includes a fuel injection control means 31
Contains.

The fuel injection control means 31 controls the timing and amount of fuel injection from the injector 11 via the injector drive circuit 34. In a specific operation state of the engine, at least the amount of fuel injected from the injector is controlled. Control is performed so that part is injected during the intake stroke. That is, in the specific operation region of the engine, the injector 11
, The fuel injection is performed in each of the intake stroke and the compression stroke, or the fuel injection is performed only in the intake stroke. For example, as will be described in detail later, split injection is performed when the catalyst is in a catalyst cold state lower than the activation temperature, and when the engine is in a cold state after the catalyst is warmed up, fuel injection is performed only in the intake stroke. Is to be performed.

The temperature condition of the catalyst and the engine is estimated by the water temperature detection signal from the water temperature sensor 26. That is, if the water temperature is lower than the first set temperature, the catalyst is in a cold state,
If the temperature is equal to or higher than the first set temperature, it is determined that the catalyst is in a warm-up state, and if the water temperature is lower than the second set temperature, it is determined that the engine is in a cold state. Usually, the second set temperature is higher than the first set temperature. In addition, the temperature state determination for determining the catalyst warm-up state may be performed by using both the detection of the water temperature and the determination of the elapsed time from the start of the engine, or by directly detecting the catalyst temperature. Is also good.

In addition to the control of the injector 11, the ECU 30 outputs a control signal to the ignition device 35 to control the ignition timing according to the operating state of the engine. Also,
The control of the intake air amount is also performed by outputting a control signal to an actuator 19 for driving the throttle valve 18. When stratified charge combustion is performed by fuel injection only during the compression stroke, the throttle is set so that the air-fuel ratio becomes lean. Control such as opening the valve 18 to increase the amount of intake air is performed. In addition, the ECU 30 controls the combustion chamber 5 during split injection or the like.
In order to generate a swirl in the intake air flow control valve 1
7 and controls the EGR valve 24 to perform EGR during stratified charge combustion with an air-fuel ratio lean.

FIG. 3 shows an example of the configuration of the fuel system.
In this figure, a fuel supply passage 37 and a fuel return passage 38 are connected between the injector 11 and the fuel tank 36, and the fuel supply passage 37
A low-pressure fuel pump 39, a filter 40, and an engine-driven high-pressure fuel pump 41 are provided in this order from the side, while a high-pressure regulator 42 and a low-pressure regulator 43 located downstream thereof are provided in the fuel return passage 38. Further, a passage 4 that bypasses the high-pressure fuel pump 41
4, a check valve 45 is provided in the passage 44, a passage 46 bypassing the high-pressure regulator 42 is provided, and a solenoid valve 47 is provided in the passage 46.

Normally, the solenoid valve 4
With the valve 7 closed, the high-pressure fuel pump 41 is operated and the high-pressure regulator 42 functions, so that the fuel pressure acting on the injector 11 is adjusted to a high pressure that allows the injection in the latter half of the compression stroke. In addition, when the engine is started when the high-pressure fuel pump 41 is not sufficiently operated, the low-pressure fuel pump 39 is driven, and the low-pressure regulator 43 functions by opening the solenoid valve 47 and bypassing the high-pressure regulator 42. In addition, the fuel pressure acting on the injector 11 is adjusted to a low pressure capable of performing the intake stroke injection.

FIG. 4 shows the injection timing when the fuel injection from the injector 11 is divided injection. As shown in this figure, the split injection includes an intake stroke injection and a compression stroke injection. In the compression stroke injection, fuel is injected in the latter half of the compression stroke. In the case of the combustion chamber structure as shown in FIG. 1, the piston 4 approaches the top dead center and the fuel injected from the injector 11 is transferred to the cavity 13 at the top of the piston. It is the timing to go inward. Specifically, the crank angle θ2 between the injection start timing and the compression top dead center is 50 °
６０60 °, that is, BTDC 50 ° -60 ° C
Fuel injection is started at a timing of about A. BTDC means before top dead center, and CA means crank angle.

On the other hand, in the intake stroke injection, the fuel is injected in the first half of the intake stroke. In comparison with the compression stroke injection, the injection is performed when the position of the piston moves away from the top dead center. 13 That is, the relationship between the crank angle θ1 between the intake top dead center and the injection start timing of the intake stroke injection and the crank angle θ2 between the injection start timing and the compression top dead center is set to satisfy θ1 ≧ θ2. . In particular, in order to suppress the adhesion of fuel to the cylinder wall, the injection start timing of the intake stroke injection is 70 ° ATDC.
CA is preferable, and a range of ATDC of 70 ° ± 20 ° CA is effective. ATDC means after top dead center.

The injection timing when the fuel injection is performed only in the intake stroke is set in the same manner as the injection timing of the intake stroke injection in the split injection.

An example of a control pattern of the direct injection engine will be described with reference to a time chart of FIG.

In FIG. 5, t ₀ is the start time of the engine start and t ₁ is the completion time of the start. During the engine start period (t _{0 to} t ₁ ), the fuel injection from the injector 11 is performed during the intake stroke injection. Only. The reason for this is that if the compression stroke injection is performed at the start of the engine, vaporization and atomization are poor and misfiring is likely to occur due to fogging of fuel into the spark plug, so the intake stroke to increase the time of vaporization and atomization Injection is preferably performed, and as described above, FIG.
This is because, in the fuel system shown in (1), the high-pressure pump does not operate sufficiently at the time of starting, so that the fuel pressure is low enough to allow the intake stroke injection.

After the engine start completion time t ₁ and when the catalyst and the engine are in a cold state, split injection is performed, that is, fuel injection from the injector 11 is performed in the intake stroke and the compression stroke. . At the time of this split injection, the air-fuel ratio of the entire combustion chamber is substantially the stoichiometric air-fuel ratio (λ ≒
While the total fuel injection amount is controlled so as to satisfy 1), a predetermined percentage of the fuel is injected at the beginning of the intake stroke, and the remaining fuel is injected at the latter stage of the compression stroke. As a result, a stoichiometric air-fuel ratio or a mixture richer than the stoichiometric air-fuel ratio is formed in the vicinity of the ignition plug 10, and a mixture leaner than the stoichiometric air-fuel ratio is formed around the stoichiometric air-fuel ratio.

In this case, a stoichiometric air-fuel ratio or a mixture richer than the stoichiometric air-fuel ratio exists in the vicinity of the ignition plug 10 to the extent that it is effective as a spark, and a lean mixture is distributed over most of the combustion chamber 5 except for the vicinity of the ignition plug 10. So that the injection amount in the intake stroke is larger than the injection amount in the compression stroke,
It is preferable to increase the ratio of the intake stroke injection to the compression stroke injection as the engine load increases.

Further, when the catalyst 1 is cooled, the injector 1
The first control of the total fuel injection amount is open control until the O ₂ sensor 21 is activated, and feedback control after the O ₂ sensor is activated. Then, the fuel injection amount is calculated according to the intake air amount so that the air-fuel ratio of the entire combustion chamber becomes substantially the stoichiometric air-fuel ratio even during the open control. However, the air-fuel ratio (A / F) at the time of this open control may be slightly lean or rich as required in the range of 13 to 17. The determination of the activity of the O ₂ sensor 21 is performed by checking the inversion of the output of the O ₂ sensor. Alternatively, when a predetermined time has elapsed since the start of the engine, the O ₂ sensor 2
1 is determined to be activated.

As for the control of the ignition timing when the catalyst is cold, the basic ignition timing such as MBT may be maintained as shown by the solid line in FIG. May be slightly retarded for a certain period of time. Particularly, when the fuel injection amount is small and the fuel injection amount is small at an extremely low load such as when the engine is idling, the pulse width is reduced to such an extent that the relationship between the pulse width and the fuel injection amount cannot maintain a linear characteristic. In such a case (two-dot chain line in FIG. 4), it is preferable to perform retardation of the ignition timing and increase correction of the air amount and the fuel injection amount.

If the engine is in a cold state after the catalyst warm-up state, the state is switched to a state in which only the intake stroke injection is performed. Further, after the engine is warmed up, the state is switched to the stratified combustion state only by the compression stroke injection. When the stratified combustion state is achieved only by the compression stroke injection, the throttle valve 18 is opened to make the air-fuel ratio lean. The switching from the split injection to the intake stroke injection may be performed with a certain time lag from the time when the catalyst is warmed up.
Switching from the intake stroke injection to the compression stroke injection may be performed with a certain time lag.

According to the in-cylinder injection engine of this embodiment as described above, when the catalyst is in a cold state after the engine is started, the fuel injection amount is controlled so that the entire combustion chamber has a substantially stoichiometric air-fuel ratio. While being performed, split injection is performed. And the injected fuel is diffused by the intake stroke injection,
An air-fuel mixture leaner than the stoichiometric air-fuel ratio is formed around the area near the ignition plug 10, and a stoichiometric air-fuel ratio or an air-fuel ratio richer than the stoichiometric air-fuel ratio is formed in the area near the ignition plug 10 by fuel injection in the latter stage of the compression stroke. An air-fuel mixture is formed.

With such a fuel supply state, H discharged from the engine body 1 to the exhaust passage 16 is
The amounts of C, CO and NOx are reduced, and the warm-up of the catalyst is promoted. These operations will be specifically described with reference to FIG.

FIGS. 6 (a) and 6 (b) show intake air in the case of an engine having an injector at an intake port, and in the in-cylinder injection type engine (direct injection engine) having an injector for directly injecting fuel into a combustion chamber. In the case where only the stroke injection is performed and the case where the split injection of the intake stroke injection and the compression stroke injection is performed in the in-cylinder injection type engine (direct injection engine), the HC emission amount and the NOx emission amount from the engine main body are respectively determined. The measurement results are shown. Also,
(C) and (d) show the measurement results of the exhaust gas temperature and the fuel efficiency in the case where only the intake stroke injection is performed and the case where the split injection is performed in the direct injection engine (direct injection engine). Is shown.

These measurement results show that the engine speed is 1
The measurement was performed under the conditions of 500 rpm, an average effective pressure of Pe = 3 kg / cm ² , and an air-fuel ratio of λ = 1 (theoretical air-fuel ratio).

The reason why the air-fuel ratio is set to λ = 1 is that when the air-fuel ratio is rich, the amount of HC emission increases, and when the air-fuel ratio is lean, it is disadvantageous in terms of combustion stability at the time of cold operation and promotion of warm-up.
Also, after the catalyst has started to exhibit a catalytic function to some extent even before the catalyst is completely warmed up, it is more advantageous to set λ = 1 in order to increase the purification performance of the catalyst as much as possible. In other words, even when the catalyst is in the cold state where the split injection is performed in this embodiment (before the catalyst is completely warmed up),
When the temperature rises to some extent, the catalyst gradually starts to function. At this time, if a three-way catalyst is used, the stoichiometric air-fuel ratio becomes H
C, CO and NOx are purified, and even a recently developed catalyst capable of purifying NOx to some extent even in a lean state has a higher NOx purification rate when it has a stoichiometric air-fuel ratio.

As shown in FIGS. 6A and 6B, when the split injection is performed by the direct injection engine, the case of the port injection engine and the case of performing the intake stroke injection by the direct injection engine are described. Compared with any of the above, both the emission amount of HC and the emission amount of NOx were significantly reduced, specifically, the emission amount of HC decreased by about 45%, and the emission amount of NOx decreased by 50% or more. Further, as shown in FIG. 3 (c), according to the split injection of the in-cylinder injection engine, the exhaust gas temperature is significantly higher (about 65 to 70 ° C.) as compared with the intake stroke injection.
Rose.

Further, as shown in FIG. 5D, the fuel consumption is slightly (4 to 5%) worse than the intake stroke injection according to the split injection of the direct injection type engine. In other words, the combustion energy is consumed for the above-mentioned increase in the exhaust gas temperature, so that the fuel efficiency is somewhat deteriorated. However, as compared with the case where the ignition timing is retarded, the degree of fuel consumption deterioration is significantly smaller. In other words, the effect of raising the exhaust gas temperature and reducing HC and NOx can be obtained by retarding the ignition timing. However, if the exhaust gas temperature is raised by about 50 ° C. only by the retardation of the ignition timing, the fuel consumption becomes 25%.
%, Compared to this, the above-described split injection significantly increases the exhaust gas temperature (about 65 to 70 ° C.) while reducing the fuel consumption by 4 to 5%.

The reason why the above-described split injection achieves the effect of reducing HC and NOx and the effect of promoting an increase in exhaust gas temperature is as follows.

When the fuel is ignited in a state where a relatively rich air-fuel mixture of λ ≦ 1 exists in the area near the spark plug 10 and a lean air-fuel mixture of λ> 1 exists around the area by the divided injection, first, the ignition plug The air-fuel mixture near 10 burns, and since this air-fuel mixture is relatively rich, the initial combustion speed increases,
Generation of NOx from the excess O ₂ is not present is suppressed. At this stage, surplus fuel exists around the spark plug.

Next, the combustion spreads to the surroundings and shifts to the main combustion state. Since the surrounding air-fuel mixture is lean, slow combustion occurs. In this case, in general, A /
NOx during combustion at a lean air-fuel ratio of about F = 16-17
Although the amount of emissions tends to increase, the excess fuel burns while depriving the lean air-fuel ratio layer of oxygen, thereby lowering the oxygen concentration in the combustion chamber, thereby suppressing the generation of NOx.
Further, when ignition and combustion are performed simply at a lean air-fuel ratio, the MBT of the ignition timing shifts to the advanced side in response to the decrease in the combustion speed. Since the combustion speed is high, it is not necessary to advance the ignition timing. This is similar to the case where the ignition timing is retarded with a lean air-fuel ratio, which also reduces NOx, and also has an effect of increasing exhaust gas temperature and reducing HC. . Further, the burned gas generated by the initial combustion is reduced to internal EG.
An R effect is brought about, whereby the effect of reducing NOx is obtained.

The surplus fuel generated near the ignition plug as described above gradually deprives the lean mixture layer of oxygen and burns, and the combustion continues until the end to form a so-called post-burning state, thereby reducing HC. And the exhaust temperature is increased.

With these phenomena, the effects of reducing HC and NOx and increasing the exhaust gas temperature can be obtained.

As described above, when the split injection is performed in the catalyst cold state, HC (and CO) from the engine and NO
The emission of x is greatly reduced, thereby improving the emission under the condition that the purifying action by the catalyst is not sufficiently obtained, and increasing the exhaust gas temperature to accelerate the warm-up of the catalyst, The period during which the catalyst cannot sufficiently purify is shortened. In addition, since the air-fuel ratio of the entire combustion chamber at the time of the split injection is set to substantially the stoichiometric air-fuel ratio, the purification performance after the temperature rises to some extent even before the complete warm-up and the catalyst starts to function can be enhanced. These actions significantly improve emissions.

The above effect can be obtained by the split injection even if the ignition timing is not necessarily retarded. However, if the ignition timing is retarded as shown by a broken line in FIG. Further, the effect of promoting the warm-up of the catalyst can be further enhanced.

Particularly, when the ignition timing is retarded and the amount of air and the amount of fuel injection are increased and the amount of fuel injection is increased and corrected at the time of extremely low load such as during idling when the fuel injection amount is extremely small, catalyst warm-up and torque control are improved. Done effectively. That is, in general, when the pulse width is smaller than a predetermined lower limit, the relationship between the pulse width and the fuel injection amount cannot maintain a linear characteristic, and sufficient fuel control accuracy cannot be obtained. If the split injection is performed at a low load, the pulse width may be smaller than the lower limit. In such a situation, when the fuel injection amount is increased and corrected, the pulse width can be maintained at or above the lower limit even if the divided injection is performed, and the fuel control accuracy can be maintained. In addition, the torque decrease due to the ignition timing retard and the torque increase due to the increase in the air amount and the fuel injection amount are canceled, and the required torque is maintained. Then, in addition to the split injection, the ignition timing is retarded and the fuel injection amount is increased, so that the exhaust gas temperature is increased and the catalyst warm-up is promoted.

However, even if the ignition timing is retarded in this manner, the retard amount is smaller than that in the case where the effect of increasing the exhaust gas temperature and the like is achieved by using only the ignition timing retard without performing the split injection. Since it can be made sufficiently small, deterioration of fuel efficiency is suppressed.

Further, after the catalyst is warmed up, until the engine is warmed up, the air-fuel ratio is switched to a state in which only the intake stroke injection is performed while maintaining the stoichiometric air-fuel ratio.
As understood from FIG. 6D, the fuel efficiency is improved as compared with the split injection. Then, after the catalyst is warmed up, the emission is kept good by the exhaust gas purifying action of the catalyst, and it is more advantageous for promoting the warming-up of the engine than when the air-fuel ratio is made lean.

After the engine is warmed up, at least at a low load, the air-fuel ratio is largely lean (for example, A / F ≧ 30).
And only the compression stroke injection is performed. As a result, stratified charge combustion is performed in a state in which the air-fuel mixture is unevenly distributed in the vicinity of the ignition plug 10, and the fuel efficiency is improved by significantly leaning while ensuring combustion stability. When the stratification is performed by the compression stroke injection as described above, the combustion stability is sufficiently improved even in the lean state where the air-fuel ratio (A / F) is about 30, and a large amount of EGR can be introduced. So E
NOx can be reduced by opening the GR valve 24 and introducing EGR from the EGR passage 23.

When the engine is running at a high speed and a high load, the intake stroke is injected to perform uniform combustion.
The air-fuel ratio is controlled to the rich side necessary to secure output. In this case, if the catalyst device is located in a position close to the engine body in the exhaust passage (for example, directly connected to the exhaust manifold), the air-fuel ratio is set to an over-rich state higher than the output air-fuel ratio in order to prevent overheating of the catalyst at high speed and high load. As a result, it is necessary to lower the exhaust gas temperature due to the latent heat of vaporization of excess fuel, which leads to deterioration of fuel efficiency. Therefore, in the present embodiment, the air-fuel ratio is changed to the output air-fuel ratio (A /
F = about 13) or leaner than this, and the catalyst device 22 is connected to the exhaust pipe 1 downstream of the exhaust manifold 16a.
The catalyst is prevented from being overheated by being provided in the middle of 6b and being kept away from the engine body 1. If the catalyst device 22 is moved away from the engine body 1 in this manner, it is disadvantageous for the catalyst warm-up after the engine is started.
C and NOx are reduced.

By the way, when the above-mentioned split injection is carried out, in the structure as shown in FIG. 1, the respective timings of the intake stroke injection and the compression stroke injection are set as shown in FIG. The state is obtained.

That is, during the compression stroke injection, the combustion chamber 5
The injection start timing is set such that the fuel injected from the injector 11 provided at the peripheral portion of the fuel injector 11 goes into the cavity 13 at the top of the piston 4, so that the injected fuel is reflected by the cavity 13 and near the spark plug 10. And a relatively rich mixture layer is formed near the ignition plug 10.

On the other hand, at the time of the intake stroke injection, the injection fuel is diffused by setting the injection timing such that the fuel injected from the injector 11 is disengaged from the cavity 13, and the fuel is uniformly distributed around the area near the spark plug 10. To form an appropriate mixture layer. In particular, by setting the injection start timing of the intake stroke injection to be ATDC 70 ° ± 20 ° CA, fuel adhesion to the cylinder wall is suppressed, and the amount of HC emission is reduced. This effect will be described with reference to data shown in FIG.

FIG. 7 shows data on the change in the fuel adhesion ratio to the cylinder wall and the change in the HC discharge amount when the intake stroke injection timing is variously changed. In the structure shown, the injection start timing of the intake stroke injection is ATDC 45 ° CA, ATDC 90 ° CA, A
In each case of TDC 135 ° CA and ATDC 180 ° CA, the ratio of fuel adhesion to the cylinder wall determined by CFD is shown, and white circles show various changes in the injection start timing of the intake stroke injection using the actual machine having the structure shown in FIG. Shows the measured data of the HC emission concentration in the case of the above. The triangle mark indicates a structure in which the injector is provided at the center of the combustion chamber to inject fuel downward, and the injection start timing of the intake stroke injection is A.
TDC 90 ° CA, ATDC 135 ° CA, ATDC1
The fuel adhesion ratio to the cylinder wall obtained by CFD for each case of 80 ° CA is shown.

As shown in this figure, when the injector is provided at the center of the combustion chamber and the fuel is injected downward, the fuel adhesion ratio does not change much even if the injection timing changes, but as shown in FIG. Is provided in the peripheral portion of the combustion chamber 5, the above-mentioned fuel adhesion ratio greatly changes depending on the injection timing, and the HC discharge amount also changes accordingly. At around 70 ° CA ATDC, the amount of HC emission is minimized. It is presumed that such a tendency occurs for the following reasons.

That is, when fuel is injected in a state where the piston 4 is very close to the top dead center, a large amount of fuel reflected at the top of the piston adheres to the cylinder wall. Piston 4
At about 70 ° CA at which ATDC is lowered at a position distant from top dead center to some extent, the reflection of the injected fuel at the top of the piston is reduced, and the fuel is drawn downward as the piston is lowered. Fuel adhesion to the cylinder wall is reduced while the fuel is diffused appropriately. Further, when the fuel is injected when the piston 4 is far away from the top dead center, the fuel directly reaches the cylinder wall and the amount of fuel adhesion increases.

The fuel adhering to the cylinder wall is hard to burn and is discharged as HC (and CO), so that the amount of HC discharge changes according to the amount of fuel adhering to the cylinder wall.

From such data, the start timing of the intake stroke injection is set to about ATDC 70 ° CA (ATDC 70 ° ± 2
If it is within the range of 0 ° CA), the amount of fuel adhering to the cylinder wall is reduced as much as possible, and the amount of HC emission during the intake stroke injection is reduced.

At the time of the split injection, the intake flow control valve 1
If the swirl is generated by closing the fuel cell 7, the combustibility of the air-fuel mixture in the combustion chamber is improved, and in particular, the combustibility of the air-fuel mixture in the lean air-fuel mixture layer due to the intake stroke injection is improved.
Emissions are further reduced.

In addition to the above-described split injection, when fuel injection is performed only in the intake stroke, such as when the engine is cold after the catalyst is warmed up, the injection timing of the intake stroke injection in the split injection is adjusted. By setting the same as the injection timing, the HC emission amount is reduced.

The control pattern of the direct injection engine is not limited to that shown in FIG. 5, but can be variously changed.

For example, as control during catalyst cooling after engine start is completed, immediately after engine start is completed, ignition timing is retarded in an intake stroke injection in order to improve vaporization and atomization of fuel. Even in this state, split injection may be performed after the engine temperature has risen to some extent.

In the above embodiment, the intake stroke injection at the stoichiometric air-fuel ratio is performed when the engine is in a cold state after the catalyst is warmed up. However, when the engine is in a cold state after the catalyst is warmed up. May be performed separately. In this way, compared to the above-described embodiment, the fuel consumption is slightly deteriorated in the period from the catalyst warm-up to the engine warm-up, but the effects of warm-up promotion and emission improvement are enhanced. That is, during this period, since the catalyst has already been activated, HC and NOx are purified at a predetermined purification rate.
If the NOx emission changes, the purified HC,
Since the amount of NOx changes, emission can be further improved by reducing the amount of HC and NOx emissions from the engine by split injection.

If split injection is performed in a low load operation range or the like even after the engine is warmed up, H
By reducing the emission amounts of C and NOx, the amounts of HC and NOx after purification by the catalyst are further reduced.

In the above embodiment, swirl is generated in the combustion chamber by controlling the intake flow control valve 17 at the time of split injection or the like, but a tumble may be generated instead of swirl. .

[0083]

According to the in-cylinder injection engine of the present invention, an ignition plug is disposed substantially at the center of the combustion chamber, and an injector is injected at a peripheral portion of the combustion chamber so as to inject fuel obliquely downward. In the arranged direct injection engine,
By setting the injection start timing when performing fuel injection in the intake stroke within a range of 70 ° ± 20 ° after the top dead center in crank angle, while appropriately diffusing the injected fuel by the intake stroke injection in the combustion chamber, Fuel adhesion to the cylinder wall can be reduced. For this reason, the emission amount of HC and CO can be reduced, and the emission can be improved.

In the specific operation range, when the fuel injection is performed in each of the intake stroke and the compression stroke, the split injection is performed.
Although a relatively rich air-fuel mixture is formed near the ignition plug and a relatively lean air-fuel mixture is formed around the air-fuel mixture, the air-fuel mixture is distributed, which is advantageous for reducing HC and NOx. Also in this case, by setting the timing of the intake stroke injection as described above, the emission amount of HC and the like can be further reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of an engine body of a direct injection engine according to an embodiment of the present invention.

FIG. 2 is a schematic view of the whole direct injection engine.

FIG. 3 is an explanatory diagram of a configuration of a fuel system.

FIG. 4 is a diagram showing injection pulses of an intake stroke injection and a compression stroke injection when split injection is performed by an injector.

FIG. 5 is a time chart showing an example of a control pattern.

FIGS. 6A and 6B are graphs showing comparison data in each case of an intake stroke injection and a split injection by a port injection engine and a direct injection engine, wherein FIG. 6A shows HC emission, FIG. 6B shows NOx emission, and FIG. Indicates the exhaust temperature, and (d) indicates the fuel efficiency.

FIG. 7 is a graph showing a change in a fuel adhesion ratio to a cylinder wall and a change in HC emission when the timing of intake stroke injection is variously changed in a direct injection engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 4 Piston 5 Combustion chamber 10 Spark plug 11 Injector 13 Cavity 17 Intake flow control valve 30 ECU 31 Fuel injection control means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/34 F02D 41/34 HF (72) Inventor Noriyuki Ota 3-1, Fuchu-cho Shinchi, Aki-gun, Hiroshima Prefecture Mazda Motor Corporation Inside

Claims (8)

[Claims] An ignition plug is disposed at a substantially central portion of a combustion chamber formed above a piston in a cylinder bore, and an injector is provided at a peripheral portion of the combustion chamber so as to inject fuel obliquely downward. In the arranged in-cylinder injection engine, while providing a fuel injection control means for controlling the injector to inject at least a part of the injected fuel in an intake stroke in a specific operation state of the engine,
An in-cylinder injection engine characterized in that the injection start timing of the fuel injection in this intake stroke is set within a range of 70 ° ± 20 ° after the top dead center in crank angle. 2. The direct injection engine according to claim 1, wherein in a specific operation state of the engine, split injection is performed in which fuel is injected from the injector during an intake stroke and a compression stroke, respectively. 3. A concave cavity is provided at the top of the piston, and in the compression stroke injection, the injection direction is directed into the cavity so that the fuel reflected by the cavity reaches the vicinity of the spark plug, while the intake stroke injection is performed. 3. The direct injection engine according to claim 2, wherein the injection direction is set so as to deviate from the cavity. 4. A crank angle (θ1) between an intake top dead center and an injection start timing of an intake stroke injection, and a crank angle (θ2) between an injection start timing of a compression stroke injection and a compression top dead center. The in-cylinder injection engine according to claim 3, wherein the relationship is set so that? 1?? 2. 5. A swirl generating means for generating a swirl in a combustion chamber, and the swirl is controlled when the fuel injection control means controls at least a part of the injected fuel from the injector during an intake stroke. 5. The direct injection engine according to claim 1, wherein the generating means is operated. 6. A tumble generating means for generating a tumble in a combustion chamber, wherein the tumble control means controls at least a part of the injected fuel from the injector to be injected in an intake stroke by the fuel injection control means. 5. The direct injection engine according to claim 1, wherein the generating means is operated. 7. A spark plug is disposed at a substantially central portion of a combustion chamber formed above a piston in a cylinder bore, and an injector is provided at a peripheral portion of the combustion chamber so as to inject fuel obliquely downward. In the arranged direct injection engine, fuel injection control means for controlling the injector to perform split injection for injecting fuel into the intake stroke and the compression stroke, respectively, in a specific operating state of the engine, and A concave cavity is provided at the top so that the injection direction is directed into the cavity during the compression stroke injection so that the fuel reflected by the cavity reaches the vicinity of the spark plug, while the injection direction deviates from the cavity during the intake stroke injection. An in-cylinder injection engine characterized in that: 8. A spark plug is disposed at a substantially central portion of a combustion chamber formed above a piston in a cylinder bore, and an injector is provided at a peripheral portion of the combustion chamber so as to inject fuel obliquely downward. In the arranged in-cylinder injection engine, fuel injection control means for performing split injection for injecting fuel into the intake stroke and the compression stroke from the injector in a specific operating state of the engine is provided, and the top of the piston is provided. Is provided with a concave cavity, so that the fuel injected by the compression stroke injection is reflected by the cavity and reaches near the spark plug, and
The relationship between the crank angle (θ1) between the intake top dead center and the injection start timing of the intake stroke injection and the crank angle (θ2) between the injection start timing of the compression stroke injection and the compression top dead center is θ1. ≧
An in-cylinder injection engine, which is set to be θ2.