JP2000297682A - Internal combustion engine of cylinder injection type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize combustion and suppress generation of hazardous substances by preliminarily injecting a small amount of fuel at the intermediate stage of compression stroke prior to main injection within the predetermined operation range of an internal combustion engine under medium load or higher, and then conducting main injection near the top dead center. SOLUTION: An ECU 21 decides the current operation state of an engine 17 based on an engine speed Ne and a target load, whether it is in a pilot injection range A of low engine speed and load, a main injection range B of medium engine speed and load or lower, or preliminary injection ranges C, D of medium engine speed and load or higher. In the operation range A, a pilot injection P is conducted in the latter stage of compression stroke of the engine 17, and then a main injection M is conducted near the top dead center of compression. In the operation range B, only the main injection M is conducted near the top dead center of compression of the engine 17. In the operation ranges C, D, a preliminary injection S is conducted in the intermediate stage of compression stroke of the engine 17, and then the main injection M is conducted near the top dead center of compression. Therefore, in the operation range C, the amount of fuel injected during the main injection M is reduced, and generation of black smoke is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection type internal combustion engine which performs two fuel injections in one cycle of combustion.

[0002]

2. Description of the Related Art A diesel engine is widely known as an internal combustion engine in which fuel is directly injected into a cylinder. This diesel engine does not spark-ignite like a gasoline engine, but injects fuel directly into air heated to a high temperature by high compression to spontaneously ignite. However, in this diesel engine, when a high load is applied, a large amount of fuel is injected into the combustion chamber in order to increase the engine output. Oxygen and nitrogen are combined in a high-pressure atmosphere to form nitrogen oxides (NOx), and the exhaust gas characteristics are reduced, thereby restricting the amount of fuel that can be injected into the combustion chamber.

[0003] In order to prevent the generation of black smoke and nitrogen oxides in the combustion chamber, Japanese Patent Application Laid-Open No.
There is one disclosed in Japanese Patent No. 36945. "Combustion method in diesel engine" disclosed in this publication
Performs a first combustion injection by combustion injection means into combustion air sucked in during an intake stroke to generate an air-fuel mixture, compresses the air-fuel mixture in a compression stroke, and then burns the air-fuel mixture at an appropriate time near a compression top dead center. The fuel is burned by performing a second combustion injection by the injection means to obtain an explosion, and the explosion stroke and the exhaust stroke are performed.

Therefore, by injecting the fuel in the intake stroke in advance, the fuel is completely vaporized in the compression stroke to be in a mixed gas state suitable for combustion, and complete combustion can be obtained.
Further, since a small amount of combustion is injected near the compression top dead center, the generation of black smoke and the generation of nitrogen oxides are suppressed by ideally performing complete combustion in an integrated manner.

[0005]

However, in the above-mentioned conventional "combustion method in a diesel engine", a large amount of the first fuel injection is performed in a low-temperature intake stroke. In this intake stroke injection, since the temperature in the cylinder is much lower than the boiling point of the fuel, the fuel adheres to the wall surface without being vaporized during flying. This wall-adhered fuel is then vaporized by the in-cylinder temperature that rises with the compression, forming an air-fuel mixture. However, a rich air-fuel mixture is generated at the wall-adhered portion, premature ignition occurs, and knock is liable to occur. Problem. There is also a problem that part of the first injected fuel adheres to the cylinder liner to dilute the engine oil and reduce engine durability. For this reason, at present, the effect of suppressing generation of black smoke and nitrogen oxide has not been sufficiently obtained.

SUMMARY OF THE INVENTION The present invention solves such a problem. A direct injection type internal combustion engine in which the generation of harmful substances is suppressed by performing at least two fuel injections in a predetermined operating region of a medium load or higher. The purpose is to provide institutions.

[0007]

According to a first aspect of the present invention, there is provided a direct injection internal combustion engine having a combustion chamber defined by a piston inserted into a cylinder of the internal combustion engine and a lower surface of a cylinder head. A fuel injection valve for directly injecting fuel is provided, and the main injection control means drives the fuel injection valve to perform main injection in the vicinity of the compression top dead center position of the piston. In the middle stage of the compression stroke before the main injection, the pre-injection control means pre-injects a smaller amount of fuel than the main injection.

Accordingly, in a predetermined operating region of the internal combustion engine at a medium load or higher, a small amount of fuel is pre-injected in the middle stage of the compression stroke before the main injection, and then the main injection is performed near the compression top dead center. It is possible to stabilize the combustion and suppress the generation of harmful substances while suppressing the adhesion of the injected fuel to the fuel cell.

The pre-injection control means pre-injects a small amount of fuel in the middle stage of the compression stroke before the main injection in a predetermined operation region where the internal load of the internal combustion engine is equal to or higher than the medium load. It is preferable to have pilot injection control means for performing preliminary injection in the vicinity. Further, when the preliminary injection control means has a pilot injection control means, it is preferable to change the timing of the preliminary injection in the next injection pattern when the operating state of the internal combustion engine shifts from a low load to a medium load or more. . 1. 1. Pre-injection pattern for directly switching from near the end of the compression stroke to injection timing in the middle of the compression stroke 2. A preliminary injection pattern in which the preliminary injection is temporarily stopped in the vicinity of the latter half of the compression stroke to perform only the main injection, and thereafter, the injection timing is switched to the injection timing only in the middle stage of the compression stroke. Pre-injection pattern that adds the injection timing in the middle of the compression stroke in addition to the injection near the latter half of the compression stroke

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of a direct injection internal combustion engine according to an embodiment of the present invention, and FIG. 2 schematically shows a fuel injection pattern for each operation region of the direct injection internal combustion engine.

In the cylinder injection type internal combustion engine of this embodiment, as shown in FIG. 1, reference numeral 11 denotes a fuel tank, which has a fuel filter 12 and a low-pressure fuel pump 13.
A high-pressure fuel pump 15 is connected to a supply path 14a of a fuel passage 14 connected to the low-pressure fuel pump 13, and a common rail 16 as an accumulator is connected downstream of the high-pressure fuel pump 15; 16 is provided with four injectors 18 as fuel injection means for injecting fuel into four combustion chambers of an engine 17. Each injector 18 is connected to the fuel tank 11 by a return path 14 b of the fuel path 14. Return paths 14 c and 14 d are connected to the upstream side of the high-pressure fuel pump 15 and the upstream side of the common rail 16 in the supply path 14 a of the fuel passage 14, respectively.
Control valves 19 and 20 are mounted on c and 14d.

Accordingly, the low-pressure fuel pump 13 pressurizes the fuel in the fuel tank 11 to some extent, and
4a, and the low-pressure fuel is further pressurized by the high-pressure fuel pump 15 to increase the fuel pressure to a predetermined pressure. At this time, the discharge pressure from the low-pressure fuel pump 13 is stabilized in a predetermined range by the low-pressure control valve 19, and the discharge pressure from the high-pressure fuel pump 15 is further stabilized in the predetermined range by the high-pressure control valve 20. And the common rail 16
The fuel of a predetermined pressure is supplied from each injector 18 of the engine 1
A predetermined amount is injected into each combustion chamber 7.

An electronic control unit (ECU) 21 having a function of a fuel injection control means has an accelerator opening APS.
, The engine speed Ne and the engine coolant temperature WT are input.
A target load Pe is determined based on the engine speed Ne and the engine speed Ne, an air-fuel ratio, a fuel injection amount, and the like are determined based on the engine speed Ne and the target load Pe, and fuel injection is performed at a predetermined injection timing. It has become. Further, a pressure sensor 22 is mounted on the common rail 16, and the detected value is determined by the ECU.
21 is input.

By the way, in this embodiment, this EC
U21 indicates that the crankshaft rotation angle is 100 ° to 40 ° before the compression top dead center when the engine speed Ne is equal to or higher than the predetermined engine speed and the load Pe is in a predetermined operation region where the load is medium or higher.
And near the compression top dead center, the injector 18 executes a two-stage injection in which a preliminary injection and a main injection are performed.
That is, the ECU 21 performs the preliminary injection when the crankshaft rotation angle is 100 ° to 40 ° before the compression top dead center, and then performs the main injection near the compression top dead center. The injection amount of the preliminary injection executed before the compression top dead center is determined by the engine speed Ne.
And a target load Pe, which is determined by a preliminary injection amount map (not shown). However, the fuel injection amount during the preliminary injection is set to be smaller than the fuel injection amount during the main injection.

The in-cylinder (combustion chamber) temperature of the engine 17 rises from the intake stroke to the compression stroke, reaches the highest temperature at the compression top dead center, and the self-ignition temperature in the cylinder increases because the in-cylinder pressure increases in the compression stroke. During this compression stroke, the pressure drops. Therefore, while the in-cylinder temperature is high to some extent, fuel is likely to evaporate, but by performing pre-injection at a time when the self-ignition temperature is lower and self-ignition is difficult, the injected fuel vaporizes immediately and adheres to the inner wall of the cylinder. At the same time, since it is a flying fuel, mixing with air is promoted, a lean mixture can be formed quickly, and premature ignition can be avoided.
In particular, in the operation region where the load is medium or higher, the piston speed becomes high and the squish flow increases, so that a flow that prevents the fuel spray of the preliminary injection from adhering to the inner wall of the cylinder is generated, and the flow of the fuel spray is opposed. As a result, agitation is promoted, and by utilizing this, a lean air-fuel mixture can be quickly generated to suppress premature ignition.

After that, when the temperature in the cylinder is high and the fuel is easily vaporized, the main injection fuel is vaporized immediately by performing the main injection at a time when self-ignition is likely to occur, and the vaporized fuel at the time of the main injection is ignited. To burn the pre-injected fuel,
Combustion can be stabilized. In particular, in the operation region where the load is medium or higher, the amount of fuel due to the main injection is large, and the diffusion combustion time is insufficient, so that black smoke is likely to be generated. And generation of nitrogen oxides can be suppressed. Therefore, premature ignition of the pre-injected fuel can be prevented, and the adhesion of the injected fuel to the cylinder inner wall can be suppressed.
Moreover, generation of black smoke and generation of nitrogen oxides can be suppressed. On the other hand, by reducing the combustion pressure, the injection amount limited by the pressure resistance limit of the engine 17 can be increased, and the output can be increased.

Here, the specific injection timing patterns of the preliminary injection and the main injection by the above-described in-cylinder injection type internal combustion engine of the present embodiment will be described.

As shown in FIG. 2, the ECU 21 determines the current engine 1 based on the engine speed Ne and the target load Pe.
7, the operation state of each of the pilot injection areas A is a low-rotation low-load low-injection state, the main injection area B is equal to or less than the middle-rotation medium load, the preliminary injection area C is equal to or more than the middle-rotation medium load,
D is determined. In the operating region A, the pilot injection P is performed in the latter half of the compression stroke of the engine 17, and thereafter, the main injection M near the compression top dead center.
I do. Therefore, rapid combustion during the main injection M is suppressed,
Vibration and noise can be reduced, and generation of harmful substances such as NOx and HC can be suppressed.

On the other hand, in the operating region B, only the main injection M is performed near the compression top dead center of the engine 17. In the operation region C and the operation region D, the preliminary injection S is performed in the middle stage of the compression stroke of the engine 17, and then the main injection M is performed in the vicinity of the compression top dead center. Accordingly, in the operation region C, the fuel injection amount of the main injection M is reduced by the preliminary injection S, so that the generation of black smoke can be suppressed. In the operation region D, the output of the engine 17 can be increased by reducing the combustion pressure. .

In the direct injection internal combustion engine of the present embodiment, the specific injection timing patterns of the preliminary injection and the main injection according to the operating range of the engine 17 are not limited to those described above. 3 and 4 schematically show a fuel injection pattern for each operating region of a direct injection internal combustion engine according to another embodiment of the present invention.

In the fuel injection pattern of this embodiment shown in FIG. 3, in the operating region A, the pilot injection P is performed in the latter half of the compression stroke of the engine 17, and then the main injection M is performed near the compression top dead center. As a result, rapid combustion during the main injection M can be suppressed, vibration and noise can be reduced, and NOx
And generation of harmful substances such as HC and HC. On the other hand, in the operating region B, the main injection M is performed in the late stage of the compression stroke of the engine 17 immediately before the main injection M, and thereafter, the main injection M is performed near the compression top dead center. Is it possible to reduce NOx by suppressing rapid combustion at M
Alternatively, fuel consumption can be improved by advancing the angle. Further, in the operation region C and the operation region D, the preliminary injection S is performed in the middle stage of the compression stroke of the engine 17, and then, the close pilot injection P is performed in the latter half of the compression stroke and immediately before the main injection M. The main injection M is performed near the compression top dead center. Therefore,
In the operation region C, the preliminary injection S and the close pilot injection P
As a result, the fuel injection amount of the main injection M is reduced, so that the generation of black smoke can be suppressed and the generation of NOx can be suppressed. In the operation region D, the output of the engine 17 can be increased by reducing the combustion pressure and the NOx can be reduced. Generation can be suppressed.

Further, in the fuel injection pattern of the present embodiment shown in FIG. 4, in the operation region A, the pilot injection P is performed in the latter half of the compression stroke of the engine 17, and thereafter, the main injection M near the compression top dead center. By doing so, rapid combustion during the main injection M is suppressed, and vibration and noise can be reduced.
Generation of harmful substances such as NOx and HC can be suppressed. On the other hand, in the operation region B, the main injection M
I do. Further, in the operation region C and the operation region D, the preliminary injection S is performed in the middle stage of the compression stroke of the engine 17, and then, the close pilot injection P is performed in the latter half of the compression stroke and immediately before the main injection M. The main injection M is performed near the compression top dead center. Accordingly, in the operating region C, the fuel injection amount of the main injection M is reduced by the preliminary injection S and the proximity pilot injection P, so that it is possible to suppress the generation of black smoke and the generation of NOx, and in the operating region D, the combustion pressure is reduced. Is reduced, the output of the engine 17 can be increased, and the generation of NOx can be suppressed.

As described above, in the in-cylinder injection type internal combustion engine of the present embodiment, the engine 17 is in a predetermined operating region where the engine is at a middle load or higher, and the in-cylinder temperature is high and fuel is easily vaporized, while spontaneous ignition occurs. Pre-injection is performed at a timing of 100 ° to 40 ° before compression top dead center, which is difficult to perform, and then main injection is performed at a time when the in-cylinder temperature is high and fuel is easily vaporized and self-ignition is likely. Therefore, the injected fuel during the preliminary injection is prevented from adhering to the inner wall of the cylinder due to the increased squish flow, and the stirring is promoted, and the pre-injection spray is prematurely ignited until the main injection spray burns. The fuel injected at the time of main injection is vaporized immediately and mixed with the fuel vaporized at the time of sub-injection and ignites, stabilizing combustion, preventing the occurrence of knocking, the generation of black smoke and the generation of nitrogen. Generation of oxides can be suppressed.

The internal combustion engine of the present invention is not limited to the above embodiment. For example, in the fuel injection pattern shown in FIG. 3, the pilot injection P is executed together with the preliminary injection S in the operation regions C and D. However, in particular, it may be set so that the pilot injection P is not executed in the operation regions C and D.

[0026]

As described in detail in the above embodiment, according to the cylinder injection type internal combustion engine of the present invention, in the predetermined operation region where the internal load of the internal combustion engine is equal to or higher than the medium load, a small amount of the compression stroke in the middle stage of the compression stroke before the main injection is performed. Pre-injection of fuel is performed, and then main injection is performed near the compression top dead center, stabilizing combustion and suppressing the generation of harmful substances while suppressing the adhesion of injected fuel to cylinder liners, etc. it can.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a direct injection internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a fuel injection pattern for each operating region of the direct injection internal combustion engine.

FIG. 3 is a schematic diagram illustrating a fuel injection pattern for each operation region of a direct injection internal combustion engine according to another embodiment of the present invention.

FIG. 4 is a schematic diagram showing a fuel injection pattern for each operation region of a direct injection internal combustion engine according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Fuel tank 13 Low-pressure fuel pump 14 Fuel passage 14a Supply path 14b, 14c, 14d Return path 15 High-pressure fuel pump 16 Common rail 17 Engine 18 Injector (fuel injection valve) 21 Electronic control unit, ECU (Main injection control means, preliminary injection) Control means)

 ──────────────────────────────────────────────────の Continuing from the front page (72) Michihiro Hatake Inventor F-term in Mitsubishi Motors Corporation, 3-3-8, Shiba 5-chome, Minato-ku, Tokyo 3G023 AA04 AA05 AA18 AB05 AC04 AD08 AD14 3G066 AA07 AB02 AC09 AD12 BA12 BA14 BA16 BA17 BA22 BA24 BA25 BA26 CC01 CD26 DA04 DA09 DB06 DB09 DC04 DC05 DC09 DC14 DC18 3G301 HA02 JA24 JA25 JA26 JA37 KA09 MA01 MA11 MA19 MA23 MA26 NC02 PA17A PA17Z PB08Z PE01Z PE03Z PE08Z PF03Z

Claims (1)

[Claims] 1. A fuel injection valve for directly injecting fuel into a combustion chamber defined by a piston inserted into a cylinder of an internal combustion engine and a lower surface of a cylinder head, and a fuel injection valve near a compression top dead center of the piston. Main injection control means for driving an injection valve to perform main injection, and pre-injecting a smaller amount of fuel than the main injection in a middle stage of a compression stroke before the main injection in a predetermined operation region of a medium load or more of the internal combustion engine. An in-cylinder injection type internal combustion engine comprising: a preliminary injection control means.